Investments (Gross Unrealized Losses Related To Available-For-Sale And Held-To-Maturity Investments) (Detail) - Fixed Maturities [Member] - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Available For Sale Securities [Abstract]
Less than 12 months, fair value	$ 394	$ 1,476
Less than 12 months, unrealized losses	(2)	(47)
12 months or longer, fair value	285	944
12 months or longer, unrealized losses	(41)	(120)
Total available-for-sale, fair value	679	2,420
Total available-for-sale, unrealized losses	(43)	(167)
U S Treasury And Government [Member]
Available For Sale Securities [Abstract]
Less than 12 months, fair value	102	231
Less than 12 months, unrealized losses	0	(1)
12 months or longer, fair value	84	278
12 months or longer, unrealized losses	(1)	(9)
Total available-for-sale, fair value	186	509
Total available-for-sale, unrealized losses	(1)	(10)
US States And Political Subdivisions [Member]
Available For Sale Securities [Abstract]
Less than 12 months, fair value	5	60
Less than 12 months, unrealized losses	0	(1)
12 months or longer, fair value	26	135
12 months or longer, unrealized losses	0	(10)
Total available-for-sale, fair value	31	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	5
Less than 12 months, unrealized losses	0	0
12 months or longer, fair value	0	2
12 months or longer, unrealized losses	0	0
Total available-for-sale, fair value	5	7
Total available-for-sale, unrealized losses	0	0
Corporate Obligations [Member]
Available For Sale Securities [Abstract]
Less than 12 months, fair value	182	900
Less than 12 months, unrealized losses	(1)	(41)
12 months or longer, fair value	55	335
12 months or longer, unrealized losses	(33)	(90)
Total available-for-sale, fair value	237	1,235
Total available-for-sale, unrealized losses	(34)	(131)
Residential Mortgage Backed Agency [Member]
Available For Sale Securities [Abstract]
Less than 12 months, fair value	35	29
Less than 12 months, unrealized losses	(1)	(1)
12 months or longer, fair value	32	118
12 months or longer, unrealized losses	0	(4)
Total available-for-sale, fair value	67	147
Total available-for-sale, unrealized losses	(1)	(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	6	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	6	45
Total available-for-sale, unrealized losses	0	(2)
Collateralized Debt Obligations [Member]
Available For Sale Securities [Abstract]
Less than 12 months, fair value	43	98
Less than 12 months, unrealized losses	0	(3)
12 months or longer, fair value	68	7
12 months or longer, unrealized losses	(2)	0
Total available-for-sale, fair value	111	105
Total available-for-sale, unrealized losses	(2)	(3)
Other Asset Backed [Member]
Available For Sale Securities [Abstract]
Less than 12 months, fair value	16	127
Less than 12 months, unrealized losses	0	0
12 months or longer, fair value	9	35
12 months or longer, unrealized losses	0	(1)
Total available-for-sale, fair value	25	162
Total available-for-sale, unrealized losses	$ 0	$ (1)