Investments (Gross Unrealized Losses Related To Available-For-Sale And Held-To-Maturity Investments) (Detail) - Fixed Maturities [Member] - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Available For Sale Securities [Abstract]
Less than 12 months, fair value	$ 761	$ 371
Less than 12 months, unrealized losses	(40)	(3)
12 months or longer, fair value	79	206
12 months or longer, unrealized losses	(23)	(8)
Total available-for-sale, fair value	840	577
Total available-for-sale, unrealized losses	(63)	(11)
U S Treasury And Government [Member]
Available For Sale Securities [Abstract]
Less than 12 months, fair value	4	148
Less than 12 months, unrealized losses	0	(1)
12 months or longer, fair value	0	79
12 months or longer, unrealized losses	0	(1)
Total available-for-sale, fair value	4	227
Total available-for-sale, unrealized losses	0	(2)
US States And Political Subdivisions [Member]
Available For Sale Securities [Abstract]
Less than 12 months, fair value	31	11
Less than 12 months, unrealized losses	0	0
12 months or longer, fair value	0	15
12 months or longer, unrealized losses	0	0
Total available-for-sale, fair value	31	26
Total available-for-sale, unrealized losses	0	0
Foreign Government Debt [Member]
Available For Sale Securities [Abstract]
Less than 12 months, fair value	7
Less than 12 months, unrealized losses	(1)
12 months or longer, fair value	0
12 months or longer, unrealized losses	0
Total available-for-sale, fair value	7
Total available-for-sale, unrealized losses	(1)
Corporate Obligations [Member]
Available For Sale Securities [Abstract]
Less than 12 months, fair value	482	53
Less than 12 months, unrealized losses	(31)	(1)
12 months or longer, fair value	6	10
12 months or longer, unrealized losses	(2)	0
Total available-for-sale, fair value	488	63
Total available-for-sale, unrealized losses	(33)	(1)
Residential Mortgage Backed Agency [Member]
Available For Sale Securities [Abstract]
Less than 12 months, fair value		62
Less than 12 months, unrealized losses		0
12 months or longer, fair value		7
12 months or longer, unrealized losses		0
Total available-for-sale, fair value		69
Total available-for-sale, unrealized losses		0
Residential Mortgage Backed Non Agency [Member]
Available For Sale Securities [Abstract]
Less than 12 months, fair value	9	0
Less than 12 months, unrealized losses	(1)	0
12 months or longer, fair value	9	11
12 months or longer, unrealized losses	(6)	(5)
Total available-for-sale, fair value	18	11
Total available-for-sale, unrealized losses	(7)	(5)
Commercial Mortgage Backed Securities [Member]
Available For Sale Securities [Abstract]
Less than 12 months, fair value	9	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	9	5
Total available-for-sale, unrealized losses	(1)	0
Collateralized Debt Obligations [Member]
Available For Sale Securities [Abstract]
Less than 12 months, fair value	49	44
Less than 12 months, unrealized losses	(4)	0
12 months or longer, fair value	64	77
12 months or longer, unrealized losses	(15)	(2)
Total available-for-sale, fair value	113	121
Total available-for-sale, unrealized losses	(19)	(2)
Other Asset Backed [Member]
Available For Sale Securities [Abstract]
Less than 12 months, fair value	170	48
Less than 12 months, unrealized losses	(2)	(1)
12 months or longer, fair value	0	7
12 months or longer, unrealized losses	0	0
Total available-for-sale, fair value	170	55
Total available-for-sale, unrealized losses	$ (2)	$ (1)