Reinsurance Reinsurance (Assumed Life Reinsurance Programs Involving Minimum Benefit Guarantees Under Annuity Contracts - Schedule Of Guaranteed Minimum Benefits Income And Expense) (Detail) (USD $) In Millions, 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
Guaranteed Minimum Benefits [Line Items]
Net premiums earned	$ 3,848	$ 4,665	$ 3,783	$ 3,381	$ 3,831	$ 4,490	$ 3,757	$ 3,309	$ 15,677	$ 15,387	$ 13,504
Policy benefits and other reserve adjustments	142	130	102	147	119	83	108	91	521	401	357
Net realized gains (losses) including OTTI	272	(60)	(394)	260	83	(760)	(73)	(45)	78	(795)	432
GMDB
Guaranteed Minimum Benefits [Line Items]
Net premiums earned									85	98	109
Policy benefits and other reserve adjustments									60	59	99
GLB
Guaranteed Minimum Benefits [Line Items]
Net premiums earned									160	163	164
Policy benefits and other reserve adjustments									61	47	29
Net realized gains (losses) including OTTI									203	(812)	(64)
Gain (loss) recognized in income									302	(696)	71
Net cash received									149	161	160
Net (increase) decrease in liability									$ 153	$ (857)	$ (89)