Investments (Gross Unrealized Losses Related To Available-For-Sale And Held-To-Maturity Investments) (Detail) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Available For Sale Securities [Abstract]
Less than 12 months, fair value	$ 1,476
Less than 12 months, unrealized losses	(47)
12 months or longer, fair value	944
12 months or longer, unrealized losses	(120)
Total available-for-sale, fair value	2,420
Total available-for-sale, unrealized losses	(167)
Variable Interest Entity Primary Beneficiary [Member]
Held To Maturity Securities [Abstract]
Less than 12 months, fair value	315
Less than 12 months, unrealized losses	0
12 months or longer, fair value	0
12 months or longer, unrealized losses	0
Total held-to-maturity, fair value	315
Total held-to-maturity, unrealized losses	0
Corporate Obligations [Member] \| Variable Interest Entity Primary Beneficiary [Member]
Held To Maturity Securities [Abstract]
Less than 12 months, fair value	315
Less than 12 months, unrealized losses	0
12 months or longer, fair value	0
12 months or longer, unrealized losses	0
Total held-to-maturity, fair value	315
Total held-to-maturity, unrealized losses	0
Fixed Maturities [Member]
Available For Sale Securities [Abstract]
Less than 12 months, fair value	1,476	$ 1,204
Less than 12 months, unrealized losses	(47)	(13)
12 months or longer, fair value	944	617
12 months or longer, unrealized losses	(120)	(93)
Total available-for-sale, fair value	2,420	1,821
Total available-for-sale, unrealized losses	(167)	(106)
Fixed Maturities [Member] \| U S Treasury And Government [Member]
Available For Sale Securities [Abstract]
Less than 12 months, fair value	231	353
Less than 12 months, unrealized losses	(1)	(1)
12 months or longer, fair value	278	124
12 months or longer, unrealized losses	(9)	(5)
Total available-for-sale, fair value	509	477
Total available-for-sale, unrealized losses	(10)	(6)
Fixed Maturities [Member] \| US States And Political Subdivisions [Member]
Available For Sale Securities [Abstract]
Less than 12 months, fair value	60	203
Less than 12 months, unrealized losses	(1)	(8)
12 months or longer, fair value	135	116
12 months or longer, unrealized losses	(10)	(4)
Total available-for-sale, fair value	195	319
Total available-for-sale, unrealized losses	(11)	(12)
Fixed Maturities [Member] \| Foreign Government Debt [Member]
Available For Sale Securities [Abstract]
Less than 12 months, fair value	5	8
Less than 12 months, unrealized losses	0	0
12 months or longer, fair value	2	0
12 months or longer, unrealized losses	0	0
Total available-for-sale, fair value	7	8
Total available-for-sale, unrealized losses	0	0
Fixed Maturities [Member] \| Corporate Obligations [Member]
Available For Sale Securities [Abstract]
Less than 12 months, fair value	900	425
Less than 12 months, unrealized losses	(41)	(3)
12 months or longer, fair value	335	163
12 months or longer, unrealized losses	(90)	(77)
Total available-for-sale, fair value	1,235	588
Total available-for-sale, unrealized losses	(131)	(80)
Fixed Maturities [Member] \| Residential Mortgage Backed Agency [Member]
Available For Sale Securities [Abstract]
Less than 12 months, fair value	29	105
Less than 12 months, unrealized losses	(1)	(1)
12 months or longer, fair value	118	156
12 months or longer, unrealized losses	(4)	(3)
Total available-for-sale, fair value	147	261
Total available-for-sale, unrealized losses	(5)	(4)
Fixed Maturities [Member] \| Residential Mortgage Backed Non Agency [Member]
Available For Sale Securities [Abstract]
Less than 12 months, fair value	2	0
Less than 12 months, unrealized losses	0	0
12 months or longer, fair value	13	14
12 months or longer, unrealized losses	(4)	(4)
Total available-for-sale, fair value	15	14
Total available-for-sale, unrealized losses	(4)	(4)
Fixed Maturities [Member] \| Commercial Mortgage Backed Securities [Member]
Available For Sale Securities [Abstract]
Less than 12 months, fair value	24	27
Less than 12 months, unrealized losses	0	0
12 months or longer, fair value	21	5
12 months or longer, unrealized losses	(2)	0
Total available-for-sale, fair value	45	32
Total available-for-sale, unrealized losses	(2)	0
Fixed Maturities [Member] \| Collateralized Debt Obligations [Member]
Available For Sale Securities [Abstract]
Less than 12 months, fair value	98	12
Less than 12 months, unrealized losses	(3)	0
12 months or longer, fair value	7	0
12 months or longer, unrealized losses	0	0
Total available-for-sale, fair value	105	12
Total available-for-sale, unrealized losses	(3)	0
Fixed Maturities [Member] \| Other Asset Backed [Member]
Available For Sale Securities [Abstract]
Less than 12 months, fair value	127	71
Less than 12 months, unrealized losses	0	0
12 months or longer, fair value	35	39
12 months or longer, unrealized losses	(1)	0
Total available-for-sale, fair value	162	110
Total available-for-sale, unrealized losses	$ (1)	$ 0

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Amount of accumulated unrealized loss on investments in debt and equity securities classified as available-for-sale that have been in a continuous loss position for twelve months or longer.

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Amount of accumulated unrealized loss on investments in debt and equity securities classified as available-for-sale in a continuous loss position.

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Amount of accumulated unrealized loss on investments in debt and equity securities classified as available-for-sale that have been in a continuous loss position for less than twelve months.

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No definition available.

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Amount of accumulated unrealized loss on investment in debt security measured at amortized cost (held-to-maturity), in continuous loss position for 12 months or longer.

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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Amount of accumulated unrealized loss on investment in debt security measured at amortized cost (held-to-maturity), in unrealized loss position.

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