Investments (Gross Unrealized Losses Related To Available-For-Sale And Held-To-Maturity Investments) (Detail) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Available For Sale Securities [Abstract]
Less than 12 months, fair value	$ 501
Less than 12 months, unrealized losses	(4)
12 months or longer, fair value	1,520
12 months or longer, unrealized losses	(80)
Total available-for-sale, fair value	2,021
Total available-for-sale, unrealized losses	(84)
Variable Interest Entity Primary Beneficiary [Member]
Held To Maturity Securities [Abstract]
Less than 12 months, fair value	0
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	0
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	0
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	0
Total held-to-maturity, unrealized losses	0
Fixed Maturities [Member]
Available For Sale Securities [Abstract]
Less than 12 months, fair value	501	$ 1,476
Less than 12 months, unrealized losses	(4)	(47)
12 months or longer, fair value	1,520	944
12 months or longer, unrealized losses	(80)	(120)
Total available-for-sale, fair value	2,021	2,420
Total available-for-sale, unrealized losses	(84)	(167)
Fixed Maturities [Member] \| U S Treasury And Government [Member]
Available For Sale Securities [Abstract]
Less than 12 months, fair value	71	231
Less than 12 months, unrealized losses	0	(1)
12 months or longer, fair value	319	278
12 months or longer, unrealized losses	(5)	(9)
Total available-for-sale, fair value	390	509
Total available-for-sale, unrealized losses	(5)	(10)
Fixed Maturities [Member] \| US States And Political Subdivisions [Member]
Available For Sale Securities [Abstract]
Less than 12 months, fair value	4	60
Less than 12 months, unrealized losses	0	(1)
12 months or longer, fair value	149	135
12 months or longer, unrealized losses	(4)	(10)
Total available-for-sale, fair value	153	195
Total available-for-sale, unrealized losses	(4)	(11)
Fixed Maturities [Member] \| Foreign Government Debt [Member]
Available For Sale Securities [Abstract]
Less than 12 months, fair value	5	5
Less than 12 months, unrealized losses	0	0
12 months or longer, fair value	2	2
12 months or longer, unrealized losses	0	0
Total available-for-sale, fair value	7	7
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	280	900
Less than 12 months, unrealized losses	(2)	(41)
12 months or longer, fair value	776	335
12 months or longer, unrealized losses	(61)	(90)
Total available-for-sale, fair value	1,056	1,235
Total available-for-sale, unrealized losses	(63)	(131)
Fixed Maturities [Member] \| Residential Mortgage Backed Agency [Member]
Available For Sale Securities [Abstract]
Less than 12 months, fair value	0	29
Less than 12 months, unrealized losses	0	(1)
12 months or longer, fair value	142	118
12 months or longer, unrealized losses	(3)	(4)
Total available-for-sale, fair value	142	147
Total available-for-sale, unrealized losses	(3)	(5)
Fixed Maturities [Member] \| Residential Mortgage Backed Non Agency [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	12	13
12 months or longer, unrealized losses	(5)	(4)
Total available-for-sale, fair value	12	15
Total available-for-sale, unrealized losses	(5)	(4)
Fixed Maturities [Member] \| Commercial Mortgage Backed Securities [Member]
Available For Sale Securities [Abstract]
Less than 12 months, fair value	15	24
Less than 12 months, unrealized losses	0	0
12 months or longer, fair value	27	21
12 months or longer, unrealized losses	(1)	(2)
Total available-for-sale, fair value	42	45
Total available-for-sale, unrealized losses	(1)	(2)
Fixed Maturities [Member] \| Collateralized Debt Obligations [Member]
Available For Sale Securities [Abstract]
Less than 12 months, fair value	88	98
Less than 12 months, unrealized losses	(2)	(3)
12 months or longer, fair value	9	7
12 months or longer, unrealized losses	(1)	0
Total available-for-sale, fair value	97	105
Total available-for-sale, unrealized losses	(3)	(3)
Fixed Maturities [Member] \| Other Asset Backed [Member]
Available For Sale Securities [Abstract]
Less than 12 months, fair value	38	127
Less than 12 months, unrealized losses	0	0
12 months or longer, fair value	84	35
12 months or longer, unrealized losses	0	(1)
Total available-for-sale, fair value	122	162
Total available-for-sale, unrealized losses	$ 0	$ (1)

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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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This item represents the aggregate fair value of investments in debt and equity securities in an unrealized loss position which are categorized neither as held-to-maturity nor trading securities.

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No definition available.

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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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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.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
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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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-Publisher FASB
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Fair value of investment in debt security measured at amortized cost (held-to-maturity), in unrealized loss position.

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