| **Benefit Plans (Reconciliation of Level 3 Plan Assets) (Details) (USD $)In Millions, unless otherwise specified** | 12 Months Ended |
|--------------------------------------------------------------------------------------------------------------------|-----------------|
||
| Corporate and other bonds [Member]                                                                                 |            |   |
| **Defined Benefit Plan Disclosure [Line Items]**                                                                   |            |   |
| Fair value of plan assets at December 31                                                                           | $ 520           | $ 447 |
| Fixed Maturities [Member]                                                                                          |            |   |
| **Defined Benefit Plan Disclosure [Line Items]**                                                                   |            |   |
| Fair value of plan assets at December 31                                                                           | 841             | 804 |
| Equity securities [Member]                                                                                         |            |   |
| **Defined Benefit Plan Disclosure [Line Items]**                                                                   |            |   |
| Fair value of plan assets at December 31                                                                           | 605             | 493 |
| Hedge Funds [Member]                                                                                               |            |   |
| **Defined Benefit Plan Disclosure [Line Items]**                                                                   |            |   |
| Fair value of plan assets at December 31                                                                           | 969             | 896 |
| Private Equity Funds [Member]                                                                                      |            |   |
| **Defined Benefit Plan Disclosure [Line Items]**                                                                   |            |   |
| Fair value of plan assets at December 31                                                                           | 114             | 62 |
| Total limited partnerships [Member]                                                                                |            |   |
| **Defined Benefit Plan Disclosure [Line Items]**                                                                   |            |   |
| Fair value of plan assets at December 31                                                                           | 1,083           | 958 |
| Investment Contracts with Insurance Company [Member]                                                               |            |   |
| **Defined Benefit Plan Disclosure [Line Items]**                                                                   |            |   |
| Fair value of plan assets at December 31                                                                           |            | 10 |
| Total assets [Member]                                                                                              |            |   |
| **Defined Benefit Plan Disclosure [Line Items]**                                                                   |            |   |
| Fair value of plan assets at December 31                                                                           | 2,656           | 2,425 |
| Fair Value, Inputs, Level 3 [Member] | Corporate and other bonds [Member]                                          |            |   |
| **Defined Benefit Plan Disclosure [Line Items]**                                                                   |            |   |
| Fair value of plan assets at January 1                                                                             | 11              | 10 |
| Defined Benefit Plan, Actual Return on Plan Assets Still Held                                                      | (1)             | 1 |
| Defined Benefit Plan, Actual Return on Plan Assets Sold During Period                                              |       |    |
| Defined Benefit Plan, Purchases, Sales, and Settlements                                                            | 5               |    |
| Defined Benefit Plan, Net transfers into (out of) Level 3                                                          |       |    |
| Fair value of plan assets at December 31                                                                           | 15              | 11 |
| Fair Value, Inputs, Level 3 [Member] | Fixed Maturities [Member]                                                   |            |   |
| **Defined Benefit Plan Disclosure [Line Items]**                                                                   |            |   |
| Fair value of plan assets at January 1                                                                             | 11              | 10 |
| Defined Benefit Plan, Actual Return on Plan Assets Still Held                                                      |       | 1 |
| Defined Benefit Plan, Actual Return on Plan Assets Sold During Period                                              | (1)             |    |
| Defined Benefit Plan, Purchases, Sales, and Settlements                                                            | 5               |    |
| Defined Benefit Plan, Net transfers into (out of) Level 3                                                          |       |    |
| Fair value of plan assets at December 31                                                                           | 15              | 11 |
| Fair Value, Inputs, Level 3 [Member] | Equity securities [Member]                                                  |            |   |
| **Defined Benefit Plan Disclosure [Line Items]**                                                                   |            |   |
| Fair value of plan assets at January 1                                                                             | 5               | 5 |
| Defined Benefit Plan, Actual Return on Plan Assets Still Held                                                      | 3               |    |
| Defined Benefit Plan, Actual Return on Plan Assets Sold During Period                                              |       |    |
| Defined Benefit Plan, Purchases, Sales, and Settlements                                                            |       |    |
| Defined Benefit Plan, Net transfers into (out of) Level 3                                                          |       |    |
| Fair value of plan assets at December 31                                                                           | 8               | 5 |
| Fair Value, Inputs, Level 3 [Member] | Hedge Funds [Member]                                                        |            |   |
| **Defined Benefit Plan Disclosure [Line Items]**                                                                   |            |   |
| Fair value of plan assets at January 1                                                                             | 359             | 330 |
| Defined Benefit Plan, Actual Return on Plan Assets Still Held                                                      | 56              | 41 |
| Defined Benefit Plan, Actual Return on Plan Assets Sold During Period                                              |       | 3 |
| Defined Benefit Plan, Purchases, Sales, and Settlements                                                            | (77)            | (15) |
| Defined Benefit Plan, Net transfers into (out of) Level 3                                                          | (16)            |    |
| Fair value of plan assets at December 31                                                                           | 322             | 359 |
| Fair Value, Inputs, Level 3 [Member] | Private Equity Funds [Member]                                               |            |   |
| **Defined Benefit Plan Disclosure [Line Items]**                                                                   |            |   |
| Fair value of plan assets at January 1                                                                             | 62              | 65 |
| Defined Benefit Plan, Actual Return on Plan Assets Still Held                                                      |       | 8 |
| Defined Benefit Plan, Actual Return on Plan Assets Sold During Period                                              |       |    |
| Defined Benefit Plan, Purchases, Sales, and Settlements                                                            | 52              | (11) |
| Defined Benefit Plan, Net transfers into (out of) Level 3                                                          |       |    |
| Fair value of plan assets at December 31                                                                           | 114             | 62 |
| Fair Value, Inputs, Level 3 [Member] | Total limited partnerships [Member]                                         |            |   |
| **Defined Benefit Plan Disclosure [Line Items]**                                                                   |            |   |
| Fair value of plan assets at January 1                                                                             | 421             | 395 |
| Defined Benefit Plan, Actual Return on Plan Assets Still Held                                                      | 56              | 49 |
| Defined Benefit Plan, Actual Return on Plan Assets Sold During Period                                              |       | 3 |
| Defined Benefit Plan, Purchases, Sales, and Settlements                                                            | (25)            | (26) |
| Defined Benefit Plan, Net transfers into (out of) Level 3                                                          | (16)            |    |
| Fair value of plan assets at December 31                                                                           | 436             | 421 |
| Fair Value, Inputs, Level 3 [Member] | Investment Contracts with Insurance Company [Member]                        |            |   |
| **Defined Benefit Plan Disclosure [Line Items]**                                                                   |            |   |
| Fair value of plan assets at January 1                                                                             | 10              | 10 |
| Defined Benefit Plan, Actual Return on Plan Assets Still Held                                                      |       |    |
| Defined Benefit Plan, Actual Return on Plan Assets Sold During Period                                              |       |    |
| Defined Benefit Plan, Purchases, Sales, and Settlements                                                            | (10)            |    |
| Defined Benefit Plan, Net transfers into (out of) Level 3                                                          |       |    |
| Fair value of plan assets at December 31                                                                           |       | 10 |
| Fair Value, Inputs, Level 3 [Member] | Total assets [Member]                                                       |            |   |
| **Defined Benefit Plan Disclosure [Line Items]**                                                                   |            |   |
| Fair value of plan assets at January 1                                                                             | 447             | 420 |
| Defined Benefit Plan, Actual Return on Plan Assets Still Held                                                      | 58              | 50 |
| Defined Benefit Plan, Actual Return on Plan Assets Sold During Period                                              |       | 3 |
| Defined Benefit Plan, Purchases, Sales, and Settlements                                                            | (30)            | (26) |
| Defined Benefit Plan, Net transfers into (out of) Level 3                                                          | (16)            |    |
| Fair value of plan assets at December 31                                                                           | $ 459           | $ 447 |

| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Actual return on plan assets, separately identifying the amount related to assets sold during the period.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (d)(iv)(02)(A) -URI http://asc.fasb.org/extlink&oid=28361610&loc=d3e1928-114920Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 5 -Subparagraph (c)(iv)(02)(A) -URI http://asc.fasb.org/extlink&oid=28361610&loc=d3e2446-114920
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Actual return on plan assets, separately identifying the amount related to assets still held at the reporting date.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (d)(iv)(02)(A) -URI http://asc.fasb.org/extlink&oid=28361610&loc=d3e1928-114920Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 5 -Subparagraph (c)(iv)(02)(A) -URI http://asc.fasb.org/extlink&oid=28361610&loc=d3e2446-114920
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| X                                                                                                                                                                         |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - 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 20 -Section 50 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=28361610&loc=d3e1928-114920Reference 2: 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=29635418&loc=d3e12355-114930
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of increase (decrease) in plan assets from purchases, sales and settlement of plan obligations.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (d)(iv)(02)(B) -URI http://asc.fasb.org/extlink&oid=28361610&loc=d3e1928-114920Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 5 -Subparagraph (c)(iv)(02)(B) -URI http://asc.fasb.org/extlink&oid=28361610&loc=d3e2446-114920
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Transfers in and out of Level 3. For example, transfers due to changes in the observability of significant inputs.
+ References
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