Investments - Fair Values and Unrealized Losses by Investment Category and by Duration of Securities' Continuous Unrealized Loss Position (Detail) - Fixed maturities - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Investments, Unrealized Loss Position
Less than 12 months Fair Value	$ 775	$ 340
Less than 12 months Unrealized Losses	28	4
12 months or more Fair Value	64	183
12 months or more Unrealized Losses	4	3
Total Fair Value	839	523
Total Unrealized Losses	32	7
Corporate
Investments, Unrealized Loss Position
Less than 12 months Fair Value	600	199
Less than 12 months Unrealized Losses	23	2
12 months or more Fair Value	62	118
12 months or more Unrealized Losses	4	3
Total Fair Value	662	317
Total Unrealized Losses	27	5
States, municipalities and political subdivisions
Investments, Unrealized Loss Position
Less than 12 months Fair Value	121	98
Less than 12 months Unrealized Losses	3	1
12 months or more Fair Value	2	10
12 months or more Unrealized Losses	0	0
Total Fair Value	123	108
Total Unrealized Losses	3	1
Commercial mortgage-backed
Investments, Unrealized Loss Position
Less than 12 months Fair Value	38	6
Less than 12 months Unrealized Losses	2	0
12 months or more Fair Value	0	0
12 months or more Unrealized Losses	0	0
Total Fair Value	38	6
Total Unrealized Losses	2	0
United States government
Investments, Unrealized Loss Position
Less than 12 months Fair Value	0	0
Less than 12 months Unrealized Losses	0	0
12 months or more Fair Value	0	4
12 months or more Unrealized Losses	0	0
Total Fair Value	0	4
Total Unrealized Losses	0	0
Foreign government
Investments, Unrealized Loss Position
Less than 12 months Fair Value	16	11
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	16	11
Total Unrealized Losses	0	0
Government-sponsored enterprises
Investments, Unrealized Loss Position
Less than 12 months Fair Value	0	26
Less than 12 months Unrealized Losses	0	1
12 months or more Fair Value	0	51
12 months or more Unrealized Losses	0	0
Total Fair Value	0	77
Total Unrealized Losses	$ 0	$ 1