Investments - Fair Values and Unrealized Losses by Investment Category and by Duration of Securities' Continuous Unrealized Loss Position (Detail) - Fixed maturities - USD ($) $ in Millions	Jun. 30, 2021	Dec. 31, 2020
Investments, Unrealized Loss Position
Less than 12 months Fair Value	$ 276	$ 406
Less than 12 months Unrealized Losses	2	8
12 months or more Fair Value	43	54
12 months or more Unrealized Losses	2	2
Total Fair Value	319	460
Total Unrealized Losses	4	10
Corporate
Investments, Unrealized Loss Position
Less than 12 months Fair Value	207	330
Less than 12 months Unrealized Losses	1	5
12 months or more Fair Value	27	46
12 months or more Unrealized Losses	1	2
Total Fair Value	234	376
Total Unrealized Losses	2	7
States, municipalities and political subdivisions
Investments, Unrealized Loss Position
Less than 12 months Fair Value	46	31
Less than 12 months Unrealized Losses	1	2
12 months or more Fair Value	7	2
12 months or more Unrealized Losses	1	0
Total Fair Value	53	33
Total Unrealized Losses	2	2
Commercial mortgage-backed
Investments, Unrealized Loss Position
Less than 12 months Fair Value	4	23
Less than 12 months Unrealized Losses	0	1
12 months or more Fair Value	9	6
12 months or more Unrealized Losses	0	0
Total Fair Value	13	29
Total Unrealized Losses	0	1
United States government
Investments, Unrealized Loss Position
Less than 12 months Fair Value	9	12
Less than 12 months Unrealized Losses	0	0
12 months or more Fair Value	0	0
12 months or more Unrealized Losses	0	0
Total Fair Value	9	12
Total Unrealized Losses	0	0
Foreign government
Investments, Unrealized Loss Position
Less than 12 months Fair Value	5	10
Less than 12 months Unrealized Losses	0	0
12 months or more Fair Value	0	0
12 months or more Unrealized Losses	0	0
Total Fair Value	5	10
Total Unrealized Losses	0	$ 0
Government-sponsored enterprises
Investments, Unrealized Loss Position
Less than 12 months Fair Value	5
Less than 12 months Unrealized Losses	0
12 months or more Fair Value	0
12 months or more Unrealized Losses	0
Total Fair Value	5
Total Unrealized Losses	$ 0