Investments - Fair Values and Unrealized Losses by Investment Category and by Duration of Securities' Continuous Unrealized Loss Position (Detail) - Fixed maturities - USD ($) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2021	Dec. 31, 2020
Investments, Unrealized Loss Position
Less than 12 months Fair Value	$ 818	$ 406
Less than 12 Months, Unrealized Loss	11	8
12 months or more, Fair Value	33	54
12 months or longer, Unrealized Loss	1	2
Total Fair Value	851	460
Gross Unrealized Loss	12	10
Corporate
Investments, Unrealized Loss Position
Less than 12 months Fair Value	647	330
Less than 12 Months, Unrealized Loss	8	5
12 months or more, Fair Value	17	46
12 months or longer, Unrealized Loss	0	2
Total Fair Value	664	376
Gross Unrealized Loss	8	7
States, municipalities and political subdivisions
Investments, Unrealized Loss Position
Less than 12 months Fair Value	154	31
Less than 12 Months, Unrealized Loss	3	2
12 months or more, Fair Value	5	2
12 months or longer, Unrealized Loss	1	0
Total Fair Value	159	33
Gross Unrealized Loss	4	2
Commercial mortgage-backed
Investments, Unrealized Loss Position
Less than 12 months Fair Value	7	23
Less than 12 Months, Unrealized Loss	0	1
12 months or more, Fair Value	11	6
12 months or longer, Unrealized Loss	0	0
Total Fair Value	18	29
Gross Unrealized Loss	0	1
United States government
Investments, Unrealized Loss Position
Less than 12 months Fair Value	6	12
Less than 12 Months, Unrealized Loss	0	0
12 months or more, Fair Value	0	0
12 months or longer, Unrealized Loss	0	0
Total Fair Value	6	12
Gross Unrealized Loss	0	0
Foreign government
Investments, Unrealized Loss Position
Less than 12 months Fair Value	0	10
Less than 12 Months, Unrealized Loss	0	0
12 months or more, Fair Value	0	0
12 months or longer, Unrealized Loss	0	0
Total Fair Value	0	10
Gross Unrealized Loss	0	0
Government-sponsored enterprises
Investments, Unrealized Loss Position
Less than 12 months Fair Value	4
Less than 12 Months, Unrealized Loss	0
12 months or more, Fair Value	0
12 months or longer, Unrealized Loss	0
Total Fair Value	4
Gross Unrealized Loss	$ 0	$ 0