Rollforward Amount of Credit Losses Recognized in Earnings for OTTI Securities Held by Company for Portion of Impairment Recognized in Other Comprehensive Income (Detail) (USD $) In Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
Gain (Loss) on Investments [Line Items]
Balance at beginning of period	$ 105	$ 76	$ 96	$ 60
Credit losses recognized into current period earnings on debt securities for which an other-than-temporary impairment was not previously recognized	2		4	4
Credit losses recognized into current period earnings on debt securities for which an other-than-temporary impairment was previously recognized	11	3	18	15
Balance at end of period	$ 118	$ 79	$ 118	$ 79