| **Quarterly Financial Data (Unaudited) (Details) (USD $)In Millions, except Per Share data, unless otherwise specified**                                                                              | 3 Months Ended                        | 12 Months Ended |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|---------------------------------------|-----------------|
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| **Quarterly Financial Data [Abstract]**                                                                                                                                                               |                                  |                 |   |  |   |  |   |  |   |  |   |  |   |  |   |  |   |  |   |  |   |
| Revenues                                                                                                                                                                                              | $ 2,378us-gaap_Revenues               |                 | $ 2,411us-gaap_Revenues |  | $ 2,440us-gaap_Revenues |  | $ 2,463us-gaap_Revenues |  | $ 2,569us-gaap_Revenues |  | $ 2,458us-gaap_Revenues |  | $ 2,450us-gaap_Revenues |  | $ 2,455us-gaap_Revenues |  | $ 9,692us-gaap_Revenues |  | $ 9,932us-gaap_Revenues |  | $ 9,364us-gaap_Revenues |
| Net income (loss)                                                                                                                                                                                     | $ 198us-gaap_NetIncomeLoss            | [1]             | $ 213us-gaap_NetIncomeLoss | [1] | $ 267us-gaap_NetIncomeLoss | [1] | $ 13us-gaap_NetIncomeLoss | [1] | $ 221us-gaap_NetIncomeLoss |  | $ 272us-gaap_NetIncomeLoss |  | $ 194us-gaap_NetIncomeLoss |  | $ 250us-gaap_NetIncomeLoss |  | $ 691us-gaap_NetIncomeLoss | [1] | $ 937us-gaap_NetIncomeLoss |  | $ 628us-gaap_NetIncomeLoss |
| Basic earnings (loss) per share                                                                                                                                                                       | $ 0.73us-gaap_EarningsPerShareBasic   |                 | $ 0.79us-gaap_EarningsPerShareBasic |  | $ 0.99us-gaap_EarningsPerShareBasic |  | $ 0.05us-gaap_EarningsPerShareBasic |  | $ 0.82us-gaap_EarningsPerShareBasic |  | $ 1.01us-gaap_EarningsPerShareBasic |  | $ 0.72us-gaap_EarningsPerShareBasic |  | $ 0.93us-gaap_EarningsPerShareBasic |  | $ 2.56us-gaap_EarningsPerShareBasic |  | $ 3.48us-gaap_EarningsPerShareBasic |  | $ 2.33us-gaap_EarningsPerShareBasic |
| Diluted earnings (loss) per share                                                                                                                                                                     | $ 0.73us-gaap_EarningsPerShareDiluted |                 | $ 0.79us-gaap_EarningsPerShareDiluted |  | $ 0.98us-gaap_EarningsPerShareDiluted |  | $ 0.05us-gaap_EarningsPerShareDiluted |  | $ 0.82us-gaap_EarningsPerShareDiluted | [2] | $ 1.01us-gaap_EarningsPerShareDiluted | [2] | $ 0.72us-gaap_EarningsPerShareDiluted | [2] | $ 0.93us-gaap_EarningsPerShareDiluted | [2] | $ 2.55us-gaap_EarningsPerShareDiluted |  | $ 3.47us-gaap_EarningsPerShareDiluted | [2] | $ 2.33us-gaap_EarningsPerShareDiluted |
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| [1]Net income in the first quarter of 2014 includes the impairment loss on the sale of CAC.[2]Due to the averaging of shares, quarterly earnings per share do not add to the total for the full year. |

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| - Definition
The amount of net income (loss) for the period per each share of common stock or unit outstanding during the reporting period.
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| - Definition
The amount of net income (loss) for the period available to each share of common stock or common unit outstanding during the reporting period and to each share or unit that would have been outstanding assuming the issuance of common shares or units for all dilutive potential common shares or units outstanding during the reporting period.
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| - Definition
The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.
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| - Definition
Amount of revenue recognized from goods sold, services rendered, insurance premiums, or other activities that constitute an earning process. Includes, but is not limited to, investment and interest income before deduction of interest expense when recognized as a component of revenue, and sales and trading gain (loss).
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