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	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Guaranteed Minimum Benefits [Line Items]
Net premiums earned	$ 7,059	$ 7,688	$ 7,405	$ 6,597	$ 4,207	$ 4,719	$ 4,360	$ 3,927	$ 28,749	$ 17,213	$ 17,426
Policy benefits and other reserve adjustments	161	155	146	126	159	89	153	142	588	543	517
Net realized gains (losses) including OTTI	$ 365	$ 100	$ (216)	$ (394)	$ (60)	$ (397)	$ 126	$ (89)	(145)	(420)	(507)
Guaranteed Minimum Death Benefit
Guaranteed Minimum Benefits [Line Items]
Net premiums earned									55	61	71
Policy benefits and other reserve adjustments									45	34	50
Guaranteed Minimum Income Benefit
Guaranteed Minimum Benefits [Line Items]
Net premiums earned									118	121	138
Policy benefits and other reserve adjustments									52	45	36
Net realized gains (losses) including OTTI									48	(203)	(213)
Gain (loss) recognized in income									114	(127)	(111)
Net cash received									79	98	125
Net (increase) decrease in liability									$ 35	$ (225)	$ (236)