Unaudited Quarterly Financial Information (Detail) (USD $) In Millions, except Per Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2011		Dec. 31, 2010		Dec. 31, 2009
Quarterly Financial Information [Line Items]
Revenues	$ 3,803	[1]	$ 3,772	[1]	$ 3,903
Income (loss) before income taxes	176		501		582
Net income (loss)	166		377		432
Net income (loss) per common share-basic	$ 1.02		$ 2.32		$ 2.66
Net income (loss) per common share-diluted	$ 1.02		$ 2.31		$ 2.65
First Quarter
Quarterly Financial Information [Line Items]
Revenues	929	[1]	887	[1]
Income (loss) before income taxes	76		85
Net income (loss)	62		68
Net income (loss) per common share-basic	$ 0.38		$ 0.42
Net income (loss) per common share-diluted	$ 0.38		$ 0.42
Second Quarter
Quarterly Financial Information [Line Items]
Revenues	975	[1]	878	[1]
Income (loss) before income taxes	(97)		21
Net income (loss)	(49)		27
Net income (loss) per common share-basic	$ (0.30)		$ 0.17
Net income (loss) per common share-diluted	$ (0.30)		$ 0.17
Third Quarter
Quarterly Financial Information [Line Items]
Revenues	944	[1]	1,071	[1]
Income (loss) before income taxes	11		221
Net income (loss)	19		156
Net income (loss) per common share-basic	$ 0.12		$ 0.95
Net income (loss) per common share-diluted	$ 0.12		$ 0.95
Fourth Quarter
Quarterly Financial Information [Line Items]
Revenues	955	[1]	936	[1]
Income (loss) before income taxes	186		174
Net income (loss)	$ 134		$ 126
Net income (loss) per common share-basic	$ 0.83		$ 0.78
Net income (loss) per common share-diluted	$ 0.83		$ 0.77

[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 81.