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Investments (Amortized Cost And Fair Value Of Available-For-Sale and Held-To-Maturity Investment Portfolios) (Detail) - USD ($) $ in Millions		Mar. 31, 2020	Dec. 31, 2019
Variable Interest Entity Primary Beneficiary [Member]
Held To Maturity Securities [Abstract]
Total held-to-maturity, amortized cost		$ 575	$ 890
Allowance for Credit Losess		(46)	0
Gross unrealized gains		43	2
Gross unrealized losses		0	0
Total held-to-maturity investments, fair value		572	892
Other-Than-Temporary Impairments	[1]		0
Corporate Obligations [Member] | Variable Interest Entity Primary Beneficiary [Member]
Held To Maturity Securities [Abstract]
Total held-to-maturity, amortized cost		575	890
Allowance for Credit Losess		(46)
Gross unrealized gains		43	2
Gross unrealized losses		0	0
Total held-to-maturity investments, fair value		572	892
Other-Than-Temporary Impairments	[1]		0
Fixed Maturities [Member]
Available For Sale Securities [Abstract]
Total available-for-sale, amortized cost		2,771	2,984
Allowance for Credit Losess		0
Gross unrealized gains		223	126
Gross unrealized losses		(63)	(11)
Total available-for-sale, fair value		2,931	3,099
Other-than-temporary impairments	[1]		0
Fixed Maturities [Member] | U S Treasury And Government [Member]
Available For Sale Securities [Abstract]
Total available-for-sale, amortized cost		758	838
Allowance for Credit Losess		0
Gross unrealized gains		101	46
Gross unrealized losses		0	(2)
Total available-for-sale, fair value		859	882
Other-than-temporary impairments	[1]		0
Fixed Maturities [Member] | US States And Political Subdivisions [Member]
Available For Sale Securities [Abstract]
Total available-for-sale, amortized cost		168	178
Allowance for Credit Losess		0
Gross unrealized gains		23	22
Gross unrealized losses		0	0
Total available-for-sale, fair value		191	200
Other-than-temporary impairments	[1]		0
Fixed Maturities [Member] | Foreign Governments [Member]
Available For Sale Securities [Abstract]
Total available-for-sale, amortized cost		10	8
Allowance for Credit Losess		0
Gross unrealized gains		0	1
Gross unrealized losses		(1)	0
Total available-for-sale, fair value		9	9
Other-than-temporary impairments	[1]		0
Fixed Maturities [Member] | Corporate Obligations [Member]
Available For Sale Securities [Abstract]
Total available-for-sale, amortized cost		1,114	1,140
Allowance for Credit Losess		0
Gross unrealized gains		90	52
Gross unrealized losses		(33)	(1)
Total available-for-sale, fair value		1,171	1,191
Other-than-temporary impairments	[1]		0
Fixed Maturities [Member] | Residential Mortgage-Backed Agency [Member]
Available For Sale Securities [Abstract]
Total available-for-sale, amortized cost		266	317
Allowance for Credit Losess		0
Gross unrealized gains		8	3
Gross unrealized losses		0	0
Total available-for-sale, fair value		274	320
Other-than-temporary impairments	[1]		0
Fixed Maturities [Member] | Residential Mortgage-Backed Non-Agency [Member]
Available For Sale Securities [Abstract]
Total available-for-sale, amortized cost		27	23
Allowance for Credit Losess		0
Gross unrealized gains		1	1
Gross unrealized losses		(7)	(5)
Total available-for-sale, fair value		21	19
Other-than-temporary impairments	[1]		0
Fixed Maturities [Member] | Commercial Mortgage-Backed [Member]
Available For Sale Securities [Abstract]
Total available-for-sale, amortized cost		20	20
Allowance for Credit Losess		0
Gross unrealized gains		0	0
Gross unrealized losses		(1)	0
Total available-for-sale, fair value		19	20
Other-than-temporary impairments	[1]		0
Fixed Maturities [Member] | Collateralized Debt Obligations [Member]
Available For Sale Securities [Abstract]
Total available-for-sale, amortized cost		131	139
Allowance for Credit Losess		0
Gross unrealized gains		0	0
Gross unrealized losses		(19)	(2)
Total available-for-sale, fair value		112	137
Other-than-temporary impairments	[1]		0
Fixed Maturities [Member] | Other Asset-Backed [Member]
Available For Sale Securities [Abstract]
Total available-for-sale, amortized cost		277	321
Allowance for Credit Losess		0
Gross unrealized gains		0	1
Gross unrealized losses		(2)	(1)
Total available-for-sale, fair value		$ 275	321
Other-than-temporary impairments	[1]		$ 0
[1] Represents unrealized gains or losses on OTTI securities recognized in AOCI, which includes the non-credit component of impairments, as well as all subsequent changes in fair value of such impaired securities reported in AOCI.

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- Definition

Unrealized gains or losses on other-than-temporarily impaired securities recognized in AOCI, which includes the non-credit component of impairments, as well as all subsequent changes in fair value of such impaired securities reported in AOCI.

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Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

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Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

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