Investments - Fair Values and Unrealized Losses by Investment Category and by Duration of Securities' Continuous Unrealized Loss Position (Detail) - Fixed maturities - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Investments, Unrealized Loss Position
Less than 12 months Fair Value	$ 2,422	$ 340
Less than 12 months Unrealized Losses	189	4
12 months or more Fair Value	55	183
12 months or more Unrealized Losses	6	3
Total Fair Value	2,477	523
Total Unrealized Losses	195	7
Corporate
Investments, Unrealized Loss Position
Less than 12 months Fair Value	2,168	199
Less than 12 months Unrealized Losses	176	2
12 months or more Fair Value	52	118
12 months or more Unrealized Losses	5	3
Total Fair Value	2,220	317
Total Unrealized Losses	181	5
States, municipalities and political subdivisions
Investments, Unrealized Loss Position
Less than 12 months Fair Value	76	98
Less than 12 months Unrealized Losses	5	1
12 months or more Fair Value	3	10
12 months or more Unrealized Losses	1	0
Total Fair Value	79	108
Total Unrealized Losses	6	1
Commercial mortgage-backed
Investments, Unrealized Loss Position
Less than 12 months Fair Value	163	6
Less than 12 months Unrealized Losses	8	0
12 months or more Fair Value	0	0
12 months or more Unrealized Losses	0	0
Total Fair Value	163	6
Total Unrealized Losses	8	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
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	15	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	15	11
Total Unrealized Losses	$ 0	$ 0