Investments (Gross Unrealized Losses Related To Available-For-Sale And Held-To-Maturity Investments) (Detail) - USD ($) $ in Millions	Sep. 30, 2016	Dec. 31, 2015
Available For Sale Securities [Abstract]
Less than 12 months, fair value	$ 651	$ 2,389
Less than 12 months, unrealized losses	(4)	(36)
12 months or longer, fair value	357	413
12 months or longer, unrealized losses	(96)	(136)
Total available-for-sale, fair value	1,008	2,802
Total available-for-sale, unrealized losses	(100)	(172)
Variable Interest Entity Primary Beneficiary [Member]
Held To Maturity Securities [Abstract]
Less than 12 months, fair value	0	1,093
Less than 12 months, unrealized losses	0	(17)
12 months or longer, fair value	573	280
12 months or longer, unrealized losses	(317)	(295)
Total held-to-maturity, fair value	573	1,373
Total held-to-maturity, unrealized losses	(317)	(312)
Corporate Obligations [Member] | Variable Interest Entity Primary Beneficiary [Member]
Held To Maturity Securities [Abstract]
Less than 12 months, fair value	0	1,093
Less than 12 months, unrealized losses	0	(17)
12 months or longer, fair value	573	280
12 months or longer, unrealized losses	(317)	(295)
Total held-to-maturity, fair value	573	1,373
Total held-to-maturity, unrealized losses	(317)	(312)
Perpetual Debt And Equity Securities [Member]
Available For Sale Securities [Abstract]
Less than 12 months, fair value	0	2
Less than 12 months, unrealized losses	0	0
12 months or longer, fair value	0	3
12 months or longer, unrealized losses	0	0
Total available-for-sale, fair value	0	5
Total available-for-sale, unrealized losses	0	0
Fixed Maturities [Member]
Available For Sale Securities [Abstract]
Less than 12 months, fair value	651	2,387
Less than 12 months, unrealized losses	(4)	(36)
12 months or longer, fair value	357	410
12 months or longer, unrealized losses	(96)	(136)
Total available-for-sale, fair value	1,008	2,797
Total available-for-sale, unrealized losses	(100)	(172)
Fixed Maturities [Member] | U S Treasury And Government [Member]
Available For Sale Securities [Abstract]
Less than 12 months, fair value	180	434
Less than 12 months, unrealized losses	(1)	(2)
12 months or longer, fair value	0	50
12 months or longer, unrealized losses	0	(1)
Total available-for-sale, fair value	180	484
Total available-for-sale, unrealized losses	(1)	(3)
Fixed Maturities [Member] | US States And Political Subdivisions [Member]
Available For Sale Securities [Abstract]
Less than 12 months, fair value	88	536
Less than 12 months, unrealized losses	(1)	(11)
12 months or longer, fair value	17	42
12 months or longer, unrealized losses	(2)	(3)
Total available-for-sale, fair value	105	578
Total available-for-sale, unrealized losses	(3)	(14)
Fixed Maturities [Member] | Foreign Government Debt [Member]
Available For Sale Securities [Abstract]
Less than 12 months, fair value	6	32
Less than 12 months, unrealized losses	0	(2)
12 months or longer, fair value	1	0
12 months or longer, unrealized losses	(1)	0
Total available-for-sale, fair value	7	32
Total available-for-sale, unrealized losses	(1)	(2)
Fixed Maturities [Member] | Corporate Obligations [Member]
Available For Sale Securities [Abstract]
Less than 12 months, fair value	214	693
Less than 12 months, unrealized losses	(2)	(14)
12 months or longer, fair value	56	78
12 months or longer, unrealized losses	(79)	(89)
Total available-for-sale, fair value	270	771
Total available-for-sale, unrealized losses	(81)	(103)
Fixed Maturities [Member] | Residential Mortgage Backed Agency [Member]
Available For Sale Securities [Abstract]
Less than 12 months, fair value	81	399
Less than 12 months, unrealized losses	0	(4)
12 months or longer, fair value	134	159
12 months or longer, unrealized losses	(1)	(5)
Total available-for-sale, fair value	215	558
Total available-for-sale, unrealized losses	(1)	(9)
Fixed Maturities [Member] | Residential Mortgage Backed Non Agency [Member]
Available For Sale Securities [Abstract]
Less than 12 months, fair value	1	24
Less than 12 months, unrealized losses	0	(2)
12 months or longer, fair value	31	17
12 months or longer, unrealized losses	(6)	(4)
Total available-for-sale, fair value	32	41
Total available-for-sale, unrealized losses	(6)	(6)
Fixed Maturities [Member] | Commercial Mortgage Backed Securities [Member]
Available For Sale Securities [Abstract]
Less than 12 months, fair value	29	25
Less than 12 months, unrealized losses	0	0
12 months or longer, fair value	4	1
12 months or longer, unrealized losses	0	0
Total available-for-sale, fair value	33	26
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	0	2
Less than 12 months, unrealized losses	0	0
12 months or longer, fair value	17	29
12 months or longer, unrealized losses	0	(18)
Total available-for-sale, fair value	17	31
Total available-for-sale, unrealized losses	0	(18)
Fixed Maturities [Member] | Other Asset Backed [Member]
Available For Sale Securities [Abstract]
Less than 12 months, fair value	52	242
Less than 12 months, unrealized losses	0	(1)
12 months or longer, fair value	97	34
12 months or longer, unrealized losses	(7)	(16)
Total available-for-sale, fair value	149	276
Total available-for-sale, unrealized losses	$ (7)	$ (17)