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, 2020	Dec. 31, 2019
Investments, Unrealized Loss Position
Less than 12 months Fair Value	$ 903	$ 340
Less than 12 months Unrealized Losses	51	4
12 months or more Fair Value	36	183
12 months or more Unrealized Losses	2	3
Total Fair Value	939	523
Total Unrealized Losses	53	7
Corporate
Investments, Unrealized Loss Position
Less than 12 months Fair Value	782	199
Less than 12 months Unrealized Losses	46	2
12 months or more Fair Value	33	118
12 months or more Unrealized Losses	1	3
Total Fair Value	815	317
Total Unrealized Losses	47	5
States, municipalities and political subdivisions
Investments, Unrealized Loss Position
Less than 12 months Fair Value	54	98
Less than 12 months Unrealized Losses	2	1
12 months or more Fair Value	3	10
12 months or more Unrealized Losses	1	0
Total Fair Value	57	108
Total Unrealized Losses	3	1
Commercial mortgage-backed
Investments, Unrealized Loss Position
Less than 12 months Fair Value	47	6
Less than 12 months Unrealized Losses	3	0
12 months or more Fair Value	0	0
12 months or more Unrealized Losses	0	0
Total Fair Value	47	6
Total Unrealized Losses	3	0
United States government
Investments, Unrealized Loss Position
Less than 12 months Fair Value	6	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	6	4
Total Unrealized Losses	0	0
Foreign government
Investments, Unrealized Loss Position
Less than 12 months Fair Value	14	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	14	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