Investments (details) - Changes in Net Unrealized Investment Gains (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Changes in net unrealized investment gains [Roll Forward]
Changes in net unrealized investment gains	$ 195	$ (2,196)	$ 336
Income tax expense (benefit)	125us-gaap_OtherComprehensiveIncomeLossTax	(770)us-gaap_OtherComprehensiveIncomeLossTax	105us-gaap_OtherComprehensiveIncomeLossTax
Change in net unrealized gain on investment securities, net of tax	70	(1,426)	231
Balance, beginning of year	810	2,236	2,005
Balance, end of year	880	810	2,236
Changes in Net Unrealized Gains on Investment Securities [Member]
Changes in net unrealized investment gains [Roll Forward]
Changes in net unrealized investment gains	978	(2,731)	362
Income tax expense (benefit)	334	(950)	130
Change in net unrealized gain on investment securities, net of tax	644	(1,781)	232
Balance, beginning of year	1,322	3,103	2,871
Balance, end of year	1,966	1,322	3,103
Changes in Net Unrealized Gains on Investment Securities [Member] \| Fixed maturities [Member]
Changes in net unrealized investment gains [Roll Forward]
Changes in net unrealized investment gains	913	(2,804)	326
Changes in Net Unrealized Gains on Investment Securities [Member] \| Equity securities [Member]
Changes in net unrealized investment gains [Roll Forward]
Changes in net unrealized investment gains	63	74	38
Changes in Net Unrealized Gains on Investment Securities [Member] \| Other investments [Member]
Changes in net unrealized investment gains [Roll Forward]
Changes in net unrealized investment gains	$ 2	$ (1)	$ (2)

- Definition

Accumulated change in equity from transactions and other events and circumstances from non-owner sources, net of tax effect, at period end. Excludes Net Income (Loss), and accumulated changes in equity from transactions resulting from investments by owners and distributions to owners. Includes foreign currency translation items, certain pension adjustments, unrealized gains and losses on certain investments in debt and equity securities, other than temporary impairment (OTTI) losses related to factors other than credit losses on available-for-sale and held-to-maturity debt securities that an entity does not intend to sell and it is not more likely than not that the entity will be required to sell before recovery of the amortized cost basis, as well as changes in the fair value of derivatives related to the effective portion of a designated cash flow hedge.

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