|**Employee Retirement Benefits**                                      | 12 Months Ended                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 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|**Compensation and Retirement Disclosure [Abstract]**                 |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  
|Employee Retirement Benefits                                          | Employee Retirement BenefitsWe sponsor a qualified defined benefit pension plan that we closed entry into for new associates as of June 30, 2008, and only participants40years of age or older as of August 31, 2008, could elect to continue to participate. During 2008, we changed the form of retirement benefit we offer some associates to a company match on contributions to a 401(k) plan as further explained below. For participants remaining in the pension plan, we continue to fund future benefit obligations. Benefits for the defined benefit pension plan are based on years of credited service and compensation level. Contributions are based on the prescribed method defined in the Pension Protection Act. Our net periodic benefit cost is based on certain actuarial assumptions and also is composed of several components that are determined using the projected unit credit actuarial cost method. The qualified plan has been amended to allow for distribution of vested balances to terminated participants.We sponsor a defined contribution plan (401(k) plan) with matching company contributions totaling$14 million,$12 millionand$11 millionduring the years2016,2015and2014, respectively. Associates who are not accruing benefits under the pension plan are eligible to receive the company match of up to6 percentof cash compensation. We also pay operating expenses for the 401(k) plan. Participants vest in the company match for the 401(k) plan afterthreeyears of eligible service.We maintain a supplemental executive retirement plan (SERP) with a benefit obligation of$15 millionatyear-end2016and$14 millionat year-end2015, which is included in the projected benefit obligation. The company also makes available to a select group of associates the CFC Top Hat Savings Plan, a nonqualified deferred compensation plan, which had a fair value of$24 millionand$21 millionatDecember 31, 2016and2015, respectively.Defined Benefit Pension Plan AssumptionsWe evaluate our pension plan assumptions annually and update them as necessary. This is a summary of the weighted-average assumptions used to determine our benefit obligations at December 31 for the plans:Qualified Pension PlanSERP2016201520162015Discount rate4.30%4.55%4.10%4.30%Rate of compensation increase2.75-3.252.75-3.252.75-3.252.75-3.25To determine the discount rate for each plan, a theoretical settlement portfolio of high-quality rated corporate bonds was chosen to provide payments approximately matching the plan’s projected benefit payments. A single interest rate for each plan was determined resulting in a discounted value of the plan's benefit payments that equates to the market value of the selected bonds. The discount rate is reflective of current market interest rate conditions and our plan's liability characteristics. Based on this analysis, we decreased the rate from the prior year by0.25percentage points for the qualified pension plan and by0.20percentage points for the SERP. Compensation increase assumptions reflect anticipated rates of inflation, real return on wage growth and merit and promotional increases. The mortality assumption was updated in 2014 to the RP-2014 Employee Mortality Tables and RP-2014 Annuitant Mortality Tables for males and females projected generationally with Scale MP-2014. During 2016 and 2015, the 2014 mortality assumption was updated to include the generational projection using Scale MP-2016 and Scale MP-2015, respectively. The updated mortality table did not have a significant impact on our consolidated financial statements as our qualified plan assumes the majority of benefits will be paid in the form of lump sums.This is a summary of the weighted-average assumptions used to determine our net periodic benefit cost for the plans:Qualified Pension PlanSERP201620152014201620152014Discount rate4.55%4.25%5.15%4.30%4.05%4.80%Expected return on plan assets7.257.257.25n/an/an/aRate of compensation increase2.75-3.252.75-3.252.75-3.252.75-3.252.75-3.252.75-3.25The discount rate was increased by0.30percentage points for the qualified pension plan and0.25percentage points for the SERP due to market interest rate conditions at the beginning of2016. The discount rate assumptions for our benefit obligation generally track with high-quality rated corporate bond yields chosen in our theoretical settlement portfolio, and yearly adjustments reflect any changes to those bond yields. We believe the expected return on plan assets is representative of the expected long-term rate of return on these assets, which is consistent with2016expectations of interest rates and based partially on the fact that the plan’s common stock holdings pay dividends. We believe this rate is representative of the expected long-term rate of return on these plan assets. We review historical actual return on plan assets when determining our expected long-term rate of return. Total portfolio return for2016was16.6percent and for2015was0.6percent. Our compensation increase assumptions in2016reflect anticipated rates of inflation, real return on wage growth and merit and promotional increases.Benefit obligation activity using an actuarial measurement date for our qualified pension plan and SERP at December 31 follows:(Dollars in millions)At December 31,20162015Change in projected benefit obligation:Benefit obligation, January 1$323$319Service cost1112Interest cost1414Actuarial loss (gain)13(3)Benefits paid(21)(19)Projected benefit obligation, December 31$340$323Change in plan assets:Fair value of plan assets, January 1$278$288Actual return on plan assets453Employer contribution136Benefits paid(21)(19)Fair value of plan assets, December 31$315$278Funded status, December 31$(25)$(45)Accumulated benefit obligation$309$293Our unfunded status improved for2016primarily due to better-than-expected return on plan assets offset by an increase in actuarial losses resulting largely from decreases in discount rate and lump sum rates.A reconciliation follows of the funded status for our qualified plan and SERP at the end of the measurement period to the amounts recognized in the consolidated balance sheets at December 31:(Dollars in millions)At December 31,20162015Pension amounts recognized in the consolidated balance sheets:Other liabilities$(25)$(45)Total$(25)$(45)Pension amounts recognized in accumulated other comprehensive income:Net actuarial loss$26$41Prior service cost—1Total$26$42Below are the components of our net periodic benefit cost, as well as other changes in plan assets and benefit obligations recognized in other comprehensive income for our qualified plan and SERP at December 31:(Dollars in millions)Years ended December 31,201620152014Net periodic benefit cost:Service cost$11$12$10Interest cost141415Expected return on plan assets(19)(18)(17)Amortization of actuarial loss and prior service cost362Other—13Net periodic benefit cost$9$15$13(Dollars in millions)Years ended December 31,201620152014Other changes in plan assets and benefit obligations recognized inother comprehensive income:Current year actuarial (gain) loss$(13)$13$21Amortization of actuarial loss(2)(6)(5)Current year prior service cost——2Amortization of prior service cost(1)(1)—Total recognized in other comprehensive (income) loss$(16)$6$18The total recognized in net periodic benefit cost and other comprehensive income (loss) was a net gain of$7 million, net cost of$21 million, and a net cost of$31 millionfor the years endedDecember 31, 2016,2015and2014, respectively. The 2016 change in the amount recognized in other comprehensive income from 2015 is largely due to better-than-expected investment return partially offset with decreases in discount and lump sum rates. The estimated costs to be amortized from AOCI into net periodic benefit cost over the next year for our plans are$2 millionin actuarial loss and less than$1 millionin prior service cost.Defined Benefit Pension Plan AssetsThe pension plan assets are managed to maximize total return over the long term while providing sufficient liquidity and current return to satisfy the cash flow requirements of the plan. The plan’s day-to-day investment decisions are managed by our internal investment department; however, overall investment strategies are discussed with our employee benefits committee. Our investment strategy, currently driven by the low interest rate environment, is to weight our portfolio towards large-cap, high-quality, dividend-growing equities that we have historically favored. As our plan matures and interest rates normalize, we expect a greater allocation to fixed-income securities to better align asset and liability market risks. Our fixed-maturity bond portfolio is investment grade. The plan does not engage in derivative transactions.Excluding cash, during2016we held approximately83 percentof our pension portfolio in domestic common equity investments. The remainder of the portfolio consisted of10 percentin states, municipalities and taxable political subdivisions fixed-maturity investments and7 percentin domestic corporate fixed-maturity investments. Our common equity portfolio consisted of22 percentin the information technology sector,20 percentin the financial sector,14 percentin the healthcare sector,10 percentin the consumer staples sector,10 percentin the consumer discretionary sector and10 percentin the industrial sector at year-end2016. No additional sectors accounted for10 percentor more of our common equity portfolio balance at year-end2016.Investments in securities are valued based on the fair value hierarchy outlined in Note 3, Fair Value Measurements. The pension plan did not have any liabilities carried at fair value during the years endedDecember 31, 2016and2015. There have been no transfers between Level 1 and Level 2 for the years endedDecember 31, 2016and2015. The following table shows the fair value hierarchy for those assets measured at fair value on a recurring basis atDecember 31, 2016and2015. Excluded from the table below is cash on hand of$11 millionand$21 millionatDecember 31, 2016and2015, respectively.(Dollars in millions)Quoted prices inactive markets foridentical assets (Level 1)Significant otherobservable inputs (Level 2)Significantunobservableinputs(Level 3)TotalAt December 31, 2016Fixed maturities, available for sale:States, municipalities and political subdivisions$—$31$—$31Corporate securities—20—20Total fixed maturities, available for sale—51—51Common equities, available for sale253——253Total$253$51$—$304At December 31, 2015Fixed maturities, available for sale:States, municipalities and political subdivisions$—$32$—$32Corporate securities—13—13Total fixed maturities, available for sale—45—45Common equities, available for sale212——212Total$212$45$—$257Our pension plan assets included232,113and267,113shares of the company’s common stock atDecember 31, 2016and2015, which had a fair value of$18 millionand$16 millionatDecember 31, 2016and2015, respectively. The defined benefit pension plan did not purchase any shares of our common stock during2016and2015. During2016and 2015, the pension plan sold35,000shares and200,000shares of the company’s common stock, respectively. The company paid less than$1 millionin 2016 and$1 millionin 2015 in cash dividends on our common stock to the pension plan.We contributed$5 millionto our qualified plan during the first quarter of2017and estimate$12 millionof benefit payments from the SERP during2017. We expect to make the following benefit payments for our qualified plan and SERP, reflecting expected future service:(Dollars in millions)Years ended December 31,201720182019202020212022 - 2026Expected future benefit payments$34$23$24$26$28$148
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                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               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                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 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                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        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                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 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                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               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                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                       
|(Dollars in millions)                                                 |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  
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                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 
|Expected future benefit payments                                      |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 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