| **Benefit Plans (Fair Value of Plan Assets Measured on a Recurring Basis) (Details) - USD ($) $ in Millions**     | Dec. 31, 2015 | Dec. 31, 2014 | Dec. 31, 2013 |
|-------------------------------------------------------------------------------------------------------------------|---------------|---------------|---------------|
| Corporate and other bonds [Member]                                                                                |          |          |          |
| **Defined Benefit Plan Disclosure [Line Items]**                                                                  |          |          |          |
| Fair value of plan assets                                                                                         | $ 465         | $ 478         |          |
| Corporate and other bonds [Member] | Fair Value, Inputs, Level 1 [Member]                                         |          |          |          |
| **Defined Benefit Plan Disclosure [Line Items]**                                                                  |          |          |          |
| Fair value of plan assets                                                                                         | 0             | 0             |          |
| Corporate and other bonds [Member] | Fair Value, Inputs, Level 2 [Member]                                         |          |          |          |
| **Defined Benefit Plan Disclosure [Line Items]**                                                                  |          |          |          |
| Fair value of plan assets                                                                                         | 455           | 463           |          |
| Corporate and other bonds [Member] | Fair Value, Inputs, Level 3 [Member]                                         |          |          |          |
| **Defined Benefit Plan Disclosure [Line Items]**                                                                  |          |          |          |
| Fair value of plan assets                                                                                         | 10            | 15            | $ 15          |
| States, municipalities and political subdivisions [Member]                                                        |          |          |          |
| **Defined Benefit Plan Disclosure [Line Items]**                                                                  |          |          |          |
| Fair value of plan assets                                                                                         | 106           | 80            |          |
| States, municipalities and political subdivisions [Member] | Fair Value, Inputs, Level 1 [Member]                 |          |          |          |
| **Defined Benefit Plan Disclosure [Line Items]**                                                                  |          |          |          |
| Fair value of plan assets                                                                                         | 0             | 0             |          |
| States, municipalities and political subdivisions [Member] | Fair Value, Inputs, Level 2 [Member]                 |          |          |          |
| **Defined Benefit Plan Disclosure [Line Items]**                                                                  |          |          |          |
| Fair value of plan assets                                                                                         | 106           | 80            |          |
| States, municipalities and political subdivisions [Member] | Fair Value, Inputs, Level 3 [Member]                 |          |          |          |
| **Defined Benefit Plan Disclosure [Line Items]**                                                                  |          |          |          |
| Fair value of plan assets                                                                                         | 0             | 0             |          |
| Residential mortgage-backed [Member]                                                                              |          |          |          |
| **Defined Benefit Plan Disclosure [Line Items]**                                                                  |          |          |          |
| Fair value of plan assets                                                                                         | 133           | 123           |          |
| Residential mortgage-backed [Member] | Fair Value, Inputs, Level 1 [Member]                                       |          |          |          |
| **Defined Benefit Plan Disclosure [Line Items]**                                                                  |          |          |          |
| Fair value of plan assets                                                                                         | 0             | 0             |          |
| Residential mortgage-backed [Member] | Fair Value, Inputs, Level 2 [Member]                                       |          |          |          |
| **Defined Benefit Plan Disclosure [Line Items]**                                                                  |          |          |          |
| Fair value of plan assets                                                                                         | 133           | 123           |          |
| Residential mortgage-backed [Member] | Fair Value, Inputs, Level 3 [Member]                                       |          |          |          |
| **Defined Benefit Plan Disclosure [Line Items]**                                                                  |          |          |          |
| Fair value of plan assets                                                                                         | 0             | 0             |          |
| Commercial Mortgage Backed Securities [Member]                                                                    |          |          |          |
| **Defined Benefit Plan Disclosure [Line Items]**                                                                  |          |          |          |
| Fair value of plan assets                                                                                         | 69            | 75            |          |
| Commercial Mortgage Backed Securities [Member] | Fair Value, Inputs, Level 1 [Member]                             |          |          |          |
| **Defined Benefit Plan Disclosure [Line Items]**                                                                  |          |          |          |
| Fair value of plan assets                                                                                         | 0             | 0             |          |
| Commercial Mortgage Backed Securities [Member] | Fair Value, Inputs, Level 2 [Member]                             |          |          |          |
| **Defined Benefit Plan Disclosure [Line Items]**                                                                  |          |          |          |
| Fair value of plan assets                                                                                         | 69            | 75            |          |
| Commercial Mortgage Backed Securities [Member] | Fair Value, Inputs, Level 3 [Member]                             |          |          |          |
| **Defined Benefit Plan Disclosure [Line Items]**                                                                  |          |          |          |
| Fair value of plan assets                                                                                         | 0             | 0             |          |
| Other asset-backed [Member]                                                                                       |          |          |          |
| **Defined Benefit Plan Disclosure [Line Items]**                                                                  |          |          |          |
| Fair value of plan assets                                                                                         | 11            | 12            |          |
| Other asset-backed [Member] | Fair Value, Inputs, Level 1 [Member]                                                |          |          |          |
| **Defined Benefit Plan Disclosure [Line Items]**                                                                  |          |          |          |
| Fair value of plan assets                                                                                         | 0             | 0             |          |
| Other asset-backed [Member] | Fair Value, Inputs, Level 2 [Member]                                                |          |          |          |
| **Defined Benefit Plan Disclosure [Line Items]**                                                                  |          |          |          |
| Fair value of plan assets                                                                                         | 11            | 12            |          |
| Other asset-backed [Member] | Fair Value, Inputs, Level 3 [Member]                                                |          |          |          |
| **Defined Benefit Plan Disclosure [Line Items]**                                                                  |          |          |          |
| Fair value of plan assets                                                                                         | 0             | 0             |          |
| Total asset-backed [Member]                                                                                       |          |          |          |
| **Defined Benefit Plan Disclosure [Line Items]**                                                                  |          |          |          |
| Fair value of plan assets                                                                                         | 213           | 210           |          |
| Total asset-backed [Member] | Fair Value, Inputs, Level 1 [Member]                                                |          |          |          |
| **Defined Benefit Plan Disclosure [Line Items]**                                                                  |          |          |          |
| Fair value of plan assets                                                                                         | 0             | 0             |          |
| Total asset-backed [Member] | Fair Value, Inputs, Level 2 [Member]                                                |          |          |          |
| **Defined Benefit Plan Disclosure [Line Items]**                                                                  |          |          |          |
| Fair value of plan assets                                                                                         | 213           | 210           |          |
| Total asset-backed [Member] | Fair Value, Inputs, Level 3 [Member]                                                |          |          |          |
| **Defined Benefit Plan Disclosure [Line Items]**                                                                  |          |          |          |
| Fair value of plan assets                                                                                         | 0             | 0             |          |
| U.S. Treasury and obligations of government-sponsored enterprises [Member]                                        |          |          |          |
| **Defined Benefit Plan Disclosure [Line Items]**                                                                  |          |          |          |
| Fair value of plan assets                                                                                         | 0             | 25            |          |
| U.S. Treasury and obligations of government-sponsored enterprises [Member] | Fair Value, Inputs, Level 1 [Member] |          |          |          |
| **Defined Benefit Plan Disclosure [Line Items]**                                                                  |          |          |          |
| Fair value of plan assets                                                                                         | 0             | 25            |          |
| U.S. Treasury and obligations of government-sponsored enterprises [Member] | Fair Value, Inputs, Level 2 [Member] |          |          |          |
| **Defined Benefit Plan Disclosure [Line Items]**                                                                  |          |          |          |
| Fair value of plan assets                                                                                         | 0             | 0             |          |
| U.S. Treasury and obligations of government-sponsored enterprises [Member] | Fair Value, Inputs, Level 3 [Member] |          |          |          |
| **Defined Benefit Plan Disclosure [Line Items]**                                                                  |          |          |          |
| Fair value of plan assets                                                                                         | 0             | 0             |          |
| Fixed Maturities [Member]                                                                                         |          |          |          |
| **Defined Benefit Plan Disclosure [Line Items]**                                                                  |          |          |          |
| Fair value of plan assets                                                                                         | 784           | 793           |          |
| Fixed Maturities [Member] | Fair Value, Inputs, Level 1 [Member]                                                  |          |          |          |
| **Defined Benefit Plan Disclosure [Line Items]**                                                                  |          |          |          |
| Fair value of plan assets                                                                                         | 0             | 25            |          |
| Fixed Maturities [Member] | Fair Value, Inputs, Level 2 [Member]                                                  |          |          |          |
| **Defined Benefit Plan Disclosure [Line Items]**                                                                  |          |          |          |
| Fair value of plan assets                                                                                         | 774           | 753           |          |
| Fixed Maturities [Member] | Fair Value, Inputs, Level 3 [Member]                                                  |          |          |          |
| **Defined Benefit Plan Disclosure [Line Items]**                                                                  |          |          |          |
| Fair value of plan assets                                                                                         | 10            | 15            | 15            |
| Equity securities [Member]                                                                                        |          |          |          |
| **Defined Benefit Plan Disclosure [Line Items]**                                                                  |          |          |          |
| Fair value of plan assets                                                                                         | 443           | 507           |          |
| Equity securities [Member] | Fair Value, Inputs, Level 1 [Member]                                                 |          |          |          |
| **Defined Benefit Plan Disclosure [Line Items]**                                                                  |          |          |          |
| Fair value of plan assets                                                                                         | 336           | 389           |          |
| Equity securities [Member] | Fair Value, Inputs, Level 2 [Member]                                                 |          |          |          |
| **Defined Benefit Plan Disclosure [Line Items]**                                                                  |          |          |          |
| Fair value of plan assets                                                                                         | 107           | 118           |          |
| Equity securities [Member] | Fair Value, Inputs, Level 3 [Member]                                                 |          |          |          |
| **Defined Benefit Plan Disclosure [Line Items]**                                                                  |          |          |          |
| Fair value of plan assets                                                                                         | 0             | 0             | 8             |
| Derivative Financial Instruments, Assets [Member]                                                                 |          |          |          |
| **Defined Benefit Plan Disclosure [Line Items]**                                                                  |          |          |          |
| Fair value of plan assets                                                                                         | 1             | 1             |          |
| Derivative Financial Instruments, Assets [Member] | Fair Value, Inputs, Level 1 [Member]                          |          |          |          |
| **Defined Benefit Plan Disclosure [Line Items]**                                                                  |          |          |          |
| Fair value of plan assets                                                                                         | 1             | 1             |          |
| Derivative Financial Instruments, Assets [Member] | Fair Value, Inputs, Level 2 [Member]                          |          |          |          |
| **Defined Benefit Plan Disclosure [Line Items]**                                                                  |          |          |          |
| Fair value of plan assets                                                                                         | 0             | 0             |          |
| Derivative Financial Instruments, Assets [Member] | Fair Value, Inputs, Level 3 [Member]                          |          |          |          |
| **Defined Benefit Plan Disclosure [Line Items]**                                                                  |          |          |          |
| Fair value of plan assets                                                                                         | 0             | 0             |          |
| Short-term Investments [Member]                                                                                   |          |          |          |
| **Defined Benefit Plan Disclosure [Line Items]**                                                                  |          |          |          |
| Fair value of plan assets                                                                                         | 52            | 134           |          |
| Short-term Investments [Member] | Fair Value, Inputs, Level 1 [Member]                                            |          |          |          |
| **Defined Benefit Plan Disclosure [Line Items]**                                                                  |          |          |          |
| Fair value of plan assets                                                                                         | 24            | 33            |          |
| Short-term Investments [Member] | Fair Value, Inputs, Level 2 [Member]                                            |          |          |          |
| **Defined Benefit Plan Disclosure [Line Items]**                                                                  |          |          |          |
| Fair value of plan assets                                                                                         | 28            | 101           |          |
| Short-term Investments [Member] | Fair Value, Inputs, Level 3 [Member]                                            |          |          |          |
| **Defined Benefit Plan Disclosure [Line Items]**                                                                  |          |          |          |
| Fair value of plan assets                                                                                         | 0             | 0             |          |
| Hedge Funds [Member]                                                                                              |          |          |          |
| **Defined Benefit Plan Disclosure [Line Items]**                                                                  |          |          |          |
| Fair value of plan assets                                                                                         | 812           | 865           |          |
| Hedge Funds [Member] | Fair Value, Inputs, Level 1 [Member]                                                       |          |          |          |
| **Defined Benefit Plan Disclosure [Line Items]**                                                                  |          |          |          |
| Fair value of plan assets                                                                                         | 0             | 0             |          |
| Hedge Funds [Member] | Fair Value, Inputs, Level 2 [Member]                                                       |          |          |          |
| **Defined Benefit Plan Disclosure [Line Items]**                                                                  |          |          |          |
| Fair value of plan assets                                                                                         | 516           | 562           |          |
| Hedge Funds [Member] | Fair Value, Inputs, Level 3 [Member]                                                       |          |          |          |
| **Defined Benefit Plan Disclosure [Line Items]**                                                                  |          |          |          |
| Fair value of plan assets                                                                                         | 296           | 303           | 322           |
| Private Equity Funds [Member]                                                                                     |          |          |          |
| **Defined Benefit Plan Disclosure [Line Items]**                                                                  |          |          |          |
| Fair value of plan assets                                                                                         | 123           | 113           |          |
| Private Equity Funds [Member] | Fair Value, Inputs, Level 1 [Member]                                              |          |          |          |
| **Defined Benefit Plan Disclosure [Line Items]**                                                                  |          |          |          |
| Fair value of plan assets                                                                                         | 0             | 0             |          |
| Private Equity Funds [Member] | Fair Value, Inputs, Level 2 [Member]                                              |          |          |          |
| **Defined Benefit Plan Disclosure [Line Items]**                                                                  |          |          |          |
| Fair value of plan assets                                                                                         | 0             | 0             |          |
| Private Equity Funds [Member] | Fair Value, Inputs, Level 3 [Member]                                              |          |          |          |
| **Defined Benefit Plan Disclosure [Line Items]**                                                                  |          |          |          |
| Fair value of plan assets                                                                                         | 123           | 113           | 114           |
| Total limited partnerships [Member]                                                                               |          |          |          |
| **Defined Benefit Plan Disclosure [Line Items]**                                                                  |          |          |          |
| Fair value of plan assets                                                                                         | 935           | 978           |          |
| Total limited partnerships [Member] | Fair Value, Inputs, Level 1 [Member]                                        |          |          |          |
| **Defined Benefit Plan Disclosure [Line Items]**                                                                  |          |          |          |
| Fair value of plan assets                                                                                         | 0             | 0             |          |
| Total limited partnerships [Member] | Fair Value, Inputs, Level 2 [Member]                                        |          |          |          |
| **Defined Benefit Plan Disclosure [Line Items]**                                                                  |          |          |          |
| Fair value of plan assets                                                                                         | 516           | 562           |          |
| Total limited partnerships [Member] | Fair Value, Inputs, Level 3 [Member]                                        |          |          |          |
| **Defined Benefit Plan Disclosure [Line Items]**                                                                  |          |          |          |
| Fair value of plan assets                                                                                         | 419           | 416           | 436           |
| Other assets [Member]                                                                                             |          |          |          |
| **Defined Benefit Plan Disclosure [Line Items]**                                                                  |          |          |          |
| Fair value of plan assets                                                                                         | 52            | 30            |          |
| Other assets [Member] | Fair Value, Inputs, Level 1 [Member]                                                      |          |          |          |
| **Defined Benefit Plan Disclosure [Line Items]**                                                                  |          |          |          |
| Fair value of plan assets                                                                                         | 0             | 0             |          |
| Other assets [Member] | Fair Value, Inputs, Level 2 [Member]                                                      |          |          |          |
| **Defined Benefit Plan Disclosure [Line Items]**                                                                  |          |          |          |
| Fair value of plan assets                                                                                         | 52            | 30            |          |
| Other assets [Member] | Fair Value, Inputs, Level 3 [Member]                                                      |          |          |          |
| **Defined Benefit Plan Disclosure [Line Items]**                                                                  |          |          |          |
| Fair value of plan assets                                                                                         | 0             | 0             |          |
| Cash [Member]                                                                                                     |          |          |          |
| **Defined Benefit Plan Disclosure [Line Items]**                                                                  |          |          |          |
| Fair value of plan assets                                                                                         |          | 13            |          |
| Cash [Member] | Fair Value, Inputs, Level 1 [Member]                                                              |          |          |          |
| **Defined Benefit Plan Disclosure [Line Items]**                                                                  |          |          |          |
| Fair value of plan assets                                                                                         |          | 13            |          |
| Cash [Member] | Fair Value, Inputs, Level 2 [Member]                                                              |          |          |          |
| **Defined Benefit Plan Disclosure [Line Items]**                                                                  |          |          |          |
| Fair value of plan assets                                                                                         |          | 0             |          |
| Cash [Member] | Fair Value, Inputs, Level 3 [Member]                                                              |          |          |          |
| **Defined Benefit Plan Disclosure [Line Items]**                                                                  |          |          |          |
| Fair value of plan assets                                                                                         |          | 0             |          |
| Total assets [Member]                                                                                             |          |          |          |
| **Defined Benefit Plan Disclosure [Line Items]**                                                                  |          |          |          |
| Fair value of plan assets                                                                                         | 2,267         | 2,456         |          |
| Total assets [Member] | Fair Value, Inputs, Level 1 [Member]                                                      |          |          |          |
| **Defined Benefit Plan Disclosure [Line Items]**                                                                  |          |          |          |
| Fair value of plan assets                                                                                         | 361           | 461           |          |
| Total assets [Member] | Fair Value, Inputs, Level 2 [Member]                                                      |          |          |          |
| **Defined Benefit Plan Disclosure [Line Items]**                                                                  |          |          |          |
| Fair value of plan assets                                                                                         | 1,477         | 1,564         |          |
| Total assets [Member] | Fair Value, Inputs, Level 3 [Member]                                                      |          |          |          |
| **Defined Benefit Plan Disclosure [Line Items]**                                                                  |          |          |          |
| Fair value of plan assets                                                                                         | $ 429         | $ 431         | $ 459         |

| X                                                                                                                                                                                                                                                                                                                                                                                                                             |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.
+ References
No definition available.
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|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Assets, usually stocks, bonds, and other investments, that have been segregated and restricted (usually in a trust) to provide benefits, at their fair value as of the measurement date. Plan assets include amounts contributed by the employer (and by employees for a contributory plan) and amounts earned from investing the contributions, less benefits paid. If a plan has liabilities other than for benefits, those non-benefit obligations may be considered as reductions of plan assets.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 30 -Section 35 -Paragraph 50 -URI http://asc.fasb.org/extlink&oid=49178875&loc=d3e12355-114930Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=58740216&loc=d3e1928-114920
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