Investments (Gross Unrealized Losses Related To Available-For-Sale And Held-To-Maturity Investments) (Detail) - Fixed Maturities [Member] - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Available For Sale Securities [Abstract]
Less than 12 months, fair value	$ 371	$ 1,476
Less than 12 months, unrealized losses	(3)	(47)
12 months or longer, fair value	206	944
12 months or longer, unrealized losses	(8)	(120)
Total available-for-sale, fair value	577	2,420
Total available-for-sale, unrealized losses	(11)	(167)
U S Treasury And Government [Member]
Available For Sale Securities [Abstract]
Less than 12 months, fair value	148	231
Less than 12 months, unrealized losses	(1)	(1)
12 months or longer, fair value	79	278
12 months or longer, unrealized losses	(1)	(9)
Total available-for-sale, fair value	227	509
Total available-for-sale, unrealized losses	(2)	(10)
US States And Political Subdivisions [Member]
Available For Sale Securities [Abstract]
Less than 12 months, fair value	11	60
Less than 12 months, unrealized losses	0	(1)
12 months or longer, fair value	15	135
12 months or longer, unrealized losses	0	(10)
Total available-for-sale, fair value	26	195
Total available-for-sale, unrealized losses	0	(11)
Foreign Government Debt [Member]
Available For Sale Securities [Abstract]
Less than 12 months, fair value		5
Less than 12 months, unrealized losses		0
12 months or longer, fair value		2
12 months or longer, unrealized losses		0
Total available-for-sale, fair value		7
Total available-for-sale, unrealized losses		0
Corporate Obligations [Member]
Available For Sale Securities [Abstract]
Less than 12 months, fair value	53	900
Less than 12 months, unrealized losses	(1)	(41)
12 months or longer, fair value	10	335
12 months or longer, unrealized losses	0	(90)
Total available-for-sale, fair value	63	1,235
Total available-for-sale, unrealized losses	(1)	(131)
Residential Mortgage Backed Agency [Member]
Available For Sale Securities [Abstract]
Less than 12 months, fair value	62	29
Less than 12 months, unrealized losses	0	(1)
12 months or longer, fair value	7	118
12 months or longer, unrealized losses	0	(4)
Total available-for-sale, fair value	69	147
Total available-for-sale, unrealized losses	0	(5)
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	11	13
12 months or longer, unrealized losses	(5)	(4)
Total available-for-sale, fair value	11	15
Total available-for-sale, unrealized losses	(5)	(4)
Commercial Mortgage Backed Securities [Member]
Available For Sale Securities [Abstract]
Less than 12 months, fair value	5	24
Less than 12 months, unrealized losses	0	0
12 months or longer, fair value	0	21
12 months or longer, unrealized losses	0	(2)
Total available-for-sale, fair value	5	45
Total available-for-sale, unrealized losses	0	(2)
Collateralized Debt Obligations [Member]
Available For Sale Securities [Abstract]
Less than 12 months, fair value	44	98
Less than 12 months, unrealized losses	0	(3)
12 months or longer, fair value	77	7
12 months or longer, unrealized losses	(2)	0
Total available-for-sale, fair value	121	105
Total available-for-sale, unrealized losses	(2)	(3)
Other Asset Backed [Member]
Available For Sale Securities [Abstract]
Less than 12 months, fair value	48	127
Less than 12 months, unrealized losses	(1)	0
12 months or longer, fair value	7	35
12 months or longer, unrealized losses	0	(1)
Total available-for-sale, fair value	55	162
Total available-for-sale, unrealized losses	$ (1)	$ (1)