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Investments (Gross Unrealized Losses Related To Available-For-Sale And Held-To-Maturity Investments) (Detail) - USD ($) $ in Millions	Mar. 31, 2017	Dec. 31, 2016
Available For Sale Securities [Abstract]
Less than 12 months, fair value	$ 2,088	$ 1,872
Less than 12 months, unrealized losses	(66)	(62)
12 months or longer, fair value	235	300
12 months or longer, unrealized losses	(73)	(86)
Total available-for-sale, fair value	2,323	2,172
Total available-for-sale, unrealized losses	(139)	(148)
Variable Interest Entity Primary Beneficiary [Member]
Held To Maturity Securities [Abstract]
Less than 12 months, fair value	0	0
Less than 12 months, unrealized losses	0	0
12 months or longer, fair value	879	876
12 months or longer, unrealized losses	(11)	(14)
Total held-to-maturity, fair value	879	876
Total held-to-maturity, unrealized losses	(11)	(14)
Corporate Obligations [Member] | Variable Interest Entity Primary Beneficiary [Member]
Held To Maturity Securities [Abstract]
Less than 12 months, fair value	0	0
Less than 12 months, unrealized losses	0	0
12 months or longer, fair value	879	876
12 months or longer, unrealized losses	(11)	(14)
Total held-to-maturity, fair value	879	876
Total held-to-maturity, unrealized losses	(11)	(14)
Perpetual Debt And Equity Securities [Member]
Available For Sale Securities [Abstract]
Less than 12 months, fair value	0	0
Less than 12 months, unrealized losses	0	0
12 months or longer, fair value	0	0
12 months or longer, unrealized losses	0	0
Total available-for-sale, fair value	0	0
Total available-for-sale, unrealized losses	0	0
Fixed Maturities [Member]
Available For Sale Securities [Abstract]
Less than 12 months, fair value	2,088	1,872
Less than 12 months, unrealized losses	(66)	(62)
12 months or longer, fair value	235	300
12 months or longer, unrealized losses	(73)	(86)
Total available-for-sale, fair value	2,323	2,172
Total available-for-sale, unrealized losses	(139)	(148)
Fixed Maturities [Member] | U S Treasury And Government [Member]
Available For Sale Securities [Abstract]
Less than 12 months, fair value	479	432
Less than 12 months, unrealized losses	(8)	(10)
12 months or longer, fair value	0	0
12 months or longer, unrealized losses	0	0
Total available-for-sale, fair value	479	432
Total available-for-sale, unrealized losses	(8)	(10)
Fixed Maturities [Member] | US States And Political Subdivisions [Member]
Available For Sale Securities [Abstract]
Less than 12 months, fair value	441	339
Less than 12 months, unrealized losses	(20)	(13)
12 months or longer, fair value	8	18
12 months or longer, unrealized losses	0	(2)
Total available-for-sale, fair value	449	357
Total available-for-sale, unrealized losses	(20)	(15)
Fixed Maturities [Member] | Foreign Government Debt [Member]
Available For Sale Securities [Abstract]
Less than 12 months, fair value	3	5
Less than 12 months, unrealized losses	(1)	0
12 months or longer, fair value	0	0
12 months or longer, unrealized losses	0	0
Total available-for-sale, fair value	3	5
Total available-for-sale, unrealized losses	(1)	0
Fixed Maturities [Member] | Corporate Obligations [Member]
Available For Sale Securities [Abstract]
Less than 12 months, fair value	549	534
Less than 12 months, unrealized losses	(26)	(29)
12 months or longer, fair value	68	52
12 months or longer, unrealized losses	(64)	(73)
Total available-for-sale, fair value	617	586
Total available-for-sale, unrealized losses	(90)	(102)
Fixed Maturities [Member] | Residential Mortgage Backed Agency [Member]
Available For Sale Securities [Abstract]
Less than 12 months, fair value	464	436
Less than 12 months, unrealized losses	(10)	(9)
12 months or longer, fair value	104	122
12 months or longer, unrealized losses	(3)	(3)
Total available-for-sale, fair value	568	558
Total available-for-sale, unrealized losses	(13)	(12)
Fixed Maturities [Member] | Residential Mortgage Backed Non Agency [Member]
Available For Sale Securities [Abstract]
Less than 12 months, fair value	11	1
Less than 12 months, unrealized losses	0	0
12 months or longer, fair value	28	29
12 months or longer, unrealized losses	(6)	(6)
Total available-for-sale, fair value	39	30
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	12	6
Less than 12 months, unrealized losses	0	0
12 months or longer, fair value	12	15
12 months or longer, unrealized losses	0	0
Total available-for-sale, fair value	24	21
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	4	7
Less than 12 months, unrealized losses	0	0
12 months or longer, fair value	13	15
12 months or longer, unrealized losses	0	0
Total available-for-sale, fair value	17	22
Total available-for-sale, unrealized losses	0	0
Fixed Maturities [Member] | Other Asset Backed [Member]
Available For Sale Securities [Abstract]
Less than 12 months, fair value	125	112
Less than 12 months, unrealized losses	(1)	(1)
12 months or longer, fair value	2	49
12 months or longer, unrealized losses	0	(2)
Total available-for-sale, fair value	127	161
Total available-for-sale, unrealized losses	$ (1)	$ (3)

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