Investments (Details 2) (USD $)	Mar. 31, 2013 item	Dec. 31, 2012
Investments
Amortized Cost	$ 22,713,000,000	$ 23,060,000,000
Fair Value	25,372,000,000	25,936,000,000
Percentage of GNMA, FNMA and FHLMC securities rated AAA	34.00%	32.00%
Number of holdings of other than GNMA, FNMA and FHLMC having greater than 10% of total equity	0
Holdings of Issuer Other Than GNMA, FNMA and FHLMC as Percentage of Shareholders Equity, Maximum	10.00%
AAA
Investments
Amortized Cost	5,405,000,000	5,680,000,000
Fair Value	5,846,000,000	6,198,000,000
Percent of Total Fair Value	23.00%	24.00%
AA
Investments
Amortized Cost	1,173,000,000	1,102,000,000
Fair Value	1,381,000,000	1,273,000,000
Percent of Total Fair Value	5.00%	5.00%
A
Investments
Amortized Cost	4,338,000,000	4,262,000,000
Fair Value	4,944,000,000	4,849,000,000
Percent of Total Fair Value	20.00%	19.00%
BBB
Investments
Amortized Cost	10,269,000,000	10,409,000,000
Fair Value	11,670,000,000	12,019,000,000
Percent of Total Fair Value	46.00%	46.00%
Below investment grade
Investments
Amortized Cost	1,526,000,000	1,605,000,000
Fair Value	1,527,000,000	1,593,000,000
Percent of Total Fair Value	6.00%	6.00%
Total fixed maturities
Investments
Fixed maturity securities as percentage of the entity's total investments	84.00%	84.00%
Amount of securities internally rated	1,400,000,000	1,500,000,000
Amortized Cost	22,711,000,000	23,058,000,000
Fair Value	$ 25,368,000,000	$ 25,932,000,000
Percent of Total Fair Value	100.00%	100.00%

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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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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