Investments (Gross Unrealized Losses Related To Available-For-Sale And Held-To-Maturity Investments) (Detail) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
Available For Sale Securities [Abstract]
Less than 12 months, fair value	$ 2,389	$ 851
Less than 12 months, unrealized losses	(36)	(2)
12 months or longer, fair value	413	1,220
12 months or longer, unrealized losses	(136)	(145)
Total available-for-sale, fair value	2,802	2,071
Total available-for-sale, unrealized losses	(172)	(147)
Held To Maturity Securities [Abstract]
Less than 12 months, fair value	1,093	0
Less than 12 months, unrealized losses	(17)	0
12 months or longer, fair value	280	373
12 months or longer, unrealized losses	(295)	(202)
Total held-to-maturity, fair value	1,373	373
Total held-to-maturity, unrealized losses	(312)	(202)
Corporate Obligations [Member] | Variable Interest Entity Primary Beneficiary [Member]
Held To Maturity Securities [Abstract]
Less than 12 months, fair value	1,093	0
Less than 12 months, unrealized losses	(17)	0
12 months or longer, fair value	280	373
12 months or longer, unrealized losses	(295)	(202)
Total held-to-maturity, fair value	1,373	373
Total held-to-maturity, unrealized losses	(312)	(202)
Perpetual Debt And Equity Securities [Member]
Available For Sale Securities [Abstract]
Less than 12 months, fair value	2	6
Less than 12 months, unrealized losses	0	0
12 months or longer, fair value	3	0
12 months or longer, unrealized losses	0	0
Total available-for-sale, fair value	5	6
Total available-for-sale, unrealized losses	0	0
Fixed Maturities [Member]
Available For Sale Securities [Abstract]
Less than 12 months, fair value	2,387	845
Less than 12 months, unrealized losses	(36)	(2)
12 months or longer, fair value	410	1,220
12 months or longer, unrealized losses	(136)	(145)
Total available-for-sale, fair value	2,797	2,065
Total available-for-sale, unrealized losses	(172)	(147)
Fixed Maturities [Member] | U S Treasury And Government [Member]
Available For Sale Securities [Abstract]
Less than 12 months, fair value	434	197
Less than 12 months, unrealized losses	(2)	0
12 months or longer, fair value	50	175
12 months or longer, unrealized losses	(1)	(3)
Total available-for-sale, fair value	484	372
Total available-for-sale, unrealized losses	(3)	(3)
Fixed Maturities [Member] | US States And Political Subdivisions [Member]
Available For Sale Securities [Abstract]
Less than 12 months, fair value	536	60
Less than 12 months, unrealized losses	(11)	(1)
12 months or longer, fair value	42	257
12 months or longer, unrealized losses	(3)	(7)
Total available-for-sale, fair value	578	317
Total available-for-sale, unrealized losses	(14)	(8)
Fixed Maturities [Member] | Foreign Government Debt [Member]
Available For Sale Securities [Abstract]
Less than 12 months, fair value	32	20
Less than 12 months, unrealized losses	(2)	0
12 months or longer, fair value	0	0
12 months or longer, unrealized losses	0	0
Total available-for-sale, fair value	32	20
Total available-for-sale, unrealized losses	(2)	0
Fixed Maturities [Member] | Corporate Obligations [Member]
Available For Sale Securities [Abstract]
Less than 12 months, fair value	693	468
Less than 12 months, unrealized losses	(14)	(1)
12 months or longer, fair value	78	251
12 months or longer, unrealized losses	(89)	(91)
Total available-for-sale, fair value	771	719
Total available-for-sale, unrealized losses	(103)	(92)
Fixed Maturities [Member] | Residential Mortgage Backed Agency [Member]
Available For Sale Securities [Abstract]
Less than 12 months, fair value	399	16
Less than 12 months, unrealized losses	(4)	0
12 months or longer, fair value	159	387
12 months or longer, unrealized losses	(5)	(7)
Total available-for-sale, fair value	558	403
Total available-for-sale, unrealized losses	(9)	(7)
Fixed Maturities [Member] | Residential Mortgage Backed Non Agency [Member]
Available For Sale Securities [Abstract]
Less than 12 months, fair value	24	10
Less than 12 months, unrealized losses	(2)	0
12 months or longer, fair value	17	19
12 months or longer, unrealized losses	(4)	(4)
Total available-for-sale, fair value	41	29
Total available-for-sale, unrealized losses	(6)	(4)
Fixed Maturities [Member] | Commercial Mortgage Backed Securities [Member]
Available For Sale Securities [Abstract]
Less than 12 months, fair value	25	4
Less than 12 months, unrealized losses	0	0
12 months or longer, fair value	1	6
12 months or longer, unrealized losses	0	0
Total available-for-sale, fair value	26	10
Total available-for-sale, unrealized losses	0	0
Fixed Maturities [Member] | Collateralized Debt Obligations [Member]
Available For Sale Securities [Abstract]
Less than 12 months, fair value	2	1
Less than 12 months, unrealized losses	0	0
12 months or longer, fair value	29	81
12 months or longer, unrealized losses	(18)	(21)
Total available-for-sale, fair value	31	82
Total available-for-sale, unrealized losses	(18)	(21)
Fixed Maturities [Member] | Other Asset Backed [Member]
Available For Sale Securities [Abstract]
Less than 12 months, fair value	242	69
Less than 12 months, unrealized losses	(1)	0
12 months or longer, fair value	34	44
12 months or longer, unrealized losses	(16)	(12)
Total available-for-sale, fair value	276	113
Total available-for-sale, unrealized losses	$ (17)	$ (12)