Investments (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Investments
Amortized Cost	$ 22,713	$ 23,060
Gross Unrealized Gains	2,752	2,978
Gross Unrealized Losses	(93)	(102)
Fair Value	25,372	25,936
Noncredit OTTI	(18)	(23)
Corporate debt securities
Investments
Amortized Cost	14,725	14,881
Gross Unrealized Gains	2,005	2,167
Gross Unrealized Losses	(10)	(7)
Fair Value	16,720	17,041
Noncredit OTTI	2
Residential mortgage backed securities
Investments
Amortized Cost	3,419	3,446
Gross Unrealized Gains	210	233
Gross Unrealized Losses	(52)	(58)
Fair Value	3,577	3,621
Noncredit OTTI	(21)	(24)
Commercial mortgage backed securities
Investments
Amortized Cost	2,578	2,717
Gross Unrealized Gains	248	287
Gross Unrealized Losses	(1)
Fair Value	2,825	3,004
State and municipal obligations
Investments
Amortized Cost	967	976
Gross Unrealized Gains	178	180
Gross Unrealized Losses	(28)	(34)
Fair Value	1,117	1,122
Asset backed securities
Investments
Amortized Cost	797	808
Gross Unrealized Gains	72	66
Gross Unrealized Losses	(2)	(3)
Fair Value	867	871
Foreign government bonds and obligations
Investments
Amortized Cost	184	188
Gross Unrealized Gains	30	36
Fair Value	214	224
U.S. government and agencies obligations
Investments
Amortized Cost	41	42
Gross Unrealized Gains	7	7
Fair Value	48	49
Total fixed maturities
Investments
Amortized Cost	22,711	23,058
Gross Unrealized Gains	2,750	2,976
Gross Unrealized Losses	(93)	(102)
Fair Value	25,368	25,932
Noncredit OTTI	(19)	(24)
Common stocks
Investments
Amortized Cost	2	2
Gross Unrealized Gains	2	2
Fair Value	4	4
Noncredit OTTI	$ 1	$ 1

Accumulated other comprehensive loss related to portion of other than temporary impairment (OTTI) due to factors other than credit losses on debt securities categorized as available-for-sale that an entity does not intend to sell and which it is not more likely than not that the entity will be required to sell before recovery of the amortized cost basis of the debt security. The amount represented by this item is net of tax, as applicable.

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This item represents the cost of debt and equity securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any.

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- Definition

This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. This item represents Available-for-sale Securities which consist of all investments in certain debt and equity securities neither classified as trading or held-to-maturity securities. A debt security represents a creditor relationship with an enterprise. Debt securities include, among other items, US Treasury securities, US government securities, municipal securities, corporate bonds, convertible debt, commercial paper, and all securitized debt instruments. An equity security represents an ownership interest in an enterprise or the right to acquire or dispose of an ownership interest in an enterprise at fixed or determinable prices. Equity securities include, among other things, common stock, certain preferred stock, warrant rights, call options, and put options, but do not include convertible debt. An entity may opt to provide the reader with additional narrative text to better understand the nature of investments in debt and equity securities which are categorized as Available-for-sale.

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- Definition

This item represents the gross unrealized gains for securities, at a point in time, which are categorized neither as held-to-maturity nor trading securities.

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