Quarterly Financial Information (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended																12 Months Ended
	Dec. 31, 2012		Sep. 30, 2012		Jun. 30, 2012		Mar. 31, 2012		Dec. 31, 2011		Sep. 30, 2011		Jun. 30, 2011		Mar. 31, 2011		Dec. 31, 2012		Dec. 31, 2011		Dec. 31, 2010
Disclosure Unaudited Quarterly Financial Information [Abstract]
Revenues	$ 1,070	[1]	$ 1,035	[1]	$ 1,020	[1]	$ 986	[1]	$ 955	[1]	$ 944	[1]	$ 975	[1]	$ 929	[1]	$ 4,111	[1]	$ 3,803	[1]	$ 3,772
Income (loss) before income taxes	273		152		29		112		186		11		(99)		75		566		173		498
Net income (loss)	$ 192		$ 111		$ 32		$ 86		$ 134		$ 19		$ (50)		$ 61		$ 421		$ 164		$ 375
Net income (loss) per common share-basic	$ 1.18		$ 0.69		$ 0.20		$ 0.53		$ 0.82		$ 0.12		$ (0.31)		$ 0.38		$ 2.59		$ 1.01		$ 2.30
Net income (loss) per common share-diluted	$ 1.17		$ 0.68		$ 0.20		$ 0.53		$ 0.82		$ 0.12		$ (0.31)		$ 0.38		$ 2.57		$ 1.01		$ 2.30

[1] Revenues including realized investment gains and losses, which are integral to our financial results over the long term, may cause this value to fluctuate substantially because we have substantial discretion in the timing of investment sales. Also, applicable accounting standards require us to recognize gains and losses from certain changes in fair values of securities and embedded derivatives without actual realization of those gains and losses. We discuss realized investment gains for the past three years in Item 7, Investments Results of Operations, Page .