Investments (Gross Unrealized Losses Related To Available-For-Sale And Held-To-Maturity Investments) (Detail) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Available For Sale Securities [Abstract]
Less than 12 months, fair value	$ 1,872	$ 2,389
Less than 12 months, unrealized losses	(62)	(36)
12 months or longer, fair value	300	413
12 months or longer, unrealized losses	(86)	(136)
Total available-for-sale, fair value	2,172	2,802
Total available-for-sale, unrealized losses	(148)	(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	876	280
12 months or longer, unrealized losses	(14)	(295)
Total held-to-maturity, fair value	876	1,373
Total held-to-maturity, unrealized losses	(14)	(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	876	280
12 months or longer, unrealized losses	(14)	(295)
Total held-to-maturity, fair value	876	1,373
Total held-to-maturity, unrealized losses	(14)	(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	1,872	2,387
Less than 12 months, unrealized losses	(62)	(36)
12 months or longer, fair value	300	410
12 months or longer, unrealized losses	(86)	(136)
Total available-for-sale, fair value	2,172	2,797
Total available-for-sale, unrealized losses	(148)	(172)
Fixed Maturities [Member] | U S Treasury And Government [Member]
Available For Sale Securities [Abstract]
Less than 12 months, fair value	432	434
Less than 12 months, unrealized losses	(10)	(2)
12 months or longer, fair value	0	50
12 months or longer, unrealized losses	0	(1)
Total available-for-sale, fair value	432	484
Total available-for-sale, unrealized losses	(10)	(3)
Fixed Maturities [Member] | US States And Political Subdivisions [Member]
Available For Sale Securities [Abstract]
Less than 12 months, fair value	339	536
Less than 12 months, unrealized losses	(13)	(11)
12 months or longer, fair value	18	42
12 months or longer, unrealized losses	(2)	(3)
Total available-for-sale, fair value	357	578
Total available-for-sale, unrealized losses	(15)	(14)
Fixed Maturities [Member] | Foreign Government Debt [Member]
Available For Sale Securities [Abstract]
Less than 12 months, fair value	5	32
Less than 12 months, unrealized losses	0	(2)
12 months or longer, fair value	0	0
12 months or longer, unrealized losses	0	0
Total available-for-sale, fair value	5	32
Total available-for-sale, unrealized losses	0	(2)
Fixed Maturities [Member] | Corporate Obligations [Member]
Available For Sale Securities [Abstract]
Less than 12 months, fair value	534	693
Less than 12 months, unrealized losses	(29)	(14)
12 months or longer, fair value	52	78
12 months or longer, unrealized losses	(73)	(89)
Total available-for-sale, fair value	586	771
Total available-for-sale, unrealized losses	(102)	(103)
Fixed Maturities [Member] | Residential Mortgage Backed Agency [Member]
Available For Sale Securities [Abstract]
Less than 12 months, fair value	436	399
Less than 12 months, unrealized losses	(9)	(4)
12 months or longer, fair value	122	159
12 months or longer, unrealized losses	(3)	(5)
Total available-for-sale, fair value	558	558
Total available-for-sale, unrealized losses	(12)	(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	29	17
12 months or longer, unrealized losses	(6)	(4)
Total available-for-sale, fair value	30	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	6	25
Less than 12 months, unrealized losses	0	0
12 months or longer, fair value	15	1
12 months or longer, unrealized losses	0	0
Total available-for-sale, fair value	21	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	7	2
Less than 12 months, unrealized losses	0	0
12 months or longer, fair value	15	29
12 months or longer, unrealized losses	0	(18)
Total available-for-sale, fair value	22	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	112	242
Less than 12 months, unrealized losses	(1)	(1)
12 months or longer, fair value	49	34
12 months or longer, unrealized losses	(2)	(16)
Total available-for-sale, fair value	161	276
Total available-for-sale, unrealized losses	$ (3)	$ (17)