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, 2019	Dec. 31, 2018
Investments, Unrealized Loss Position
Less than 12 months Fair Value	$ 104	$ 3,031
Less than 12 months Unrealized Losses	2	70
12 months or more Fair Value	441	1,149
12 months or more Unrealized Losses	12	58
Total Fair Value	545	4,180
Total Unrealized Losses	14	128
Corporate
Investments, Unrealized Loss Position
Less than 12 months Fair Value	78	2,082
Less than 12 months Unrealized Losses	2	51
12 months or more Fair Value	294	501
12 months or more Unrealized Losses	11	36
Total Fair Value	372	2,583
Total Unrealized Losses	13	87
States, municipalities and political subdivisions
Investments, Unrealized Loss Position
Less than 12 months Fair Value	13	823
Less than 12 months Unrealized Losses	0	18
12 months or more Fair Value	21	340
12 months or more Unrealized Losses	0	13
Total Fair Value	34	1,163
Total Unrealized Losses	0	31
Commercial mortgage-backed
Investments, Unrealized Loss Position
Less than 12 months Fair Value	0	77
Less than 12 months Unrealized Losses	0	0
12 months or more Fair Value	5	64
12 months or more Unrealized Losses	0	2
Total Fair Value	5	141
Total Unrealized Losses	0	2
Government-sponsored enterprises
Investments, Unrealized Loss Position
Less than 12 months Fair Value	7	49
Less than 12 months Unrealized Losses	0	1
12 months or more Fair Value	117	211
12 months or more Unrealized Losses	1	6
Total Fair Value	124	260
Total Unrealized Losses	1	7
United States government
Investments, Unrealized Loss Position
Less than 12 months Fair Value	5	0
Less than 12 months Unrealized Losses	0	0
12 months or more Fair Value	4	33
12 months or more Unrealized Losses	0	1
Total Fair Value	9	33
Total Unrealized Losses	0	$ 1
Foreign government
Investments, Unrealized Loss Position
Less than 12 months Fair Value	1
Less than 12 months Unrealized Losses	0
12 months or more Fair Value	0
12 months or more Unrealized Losses	0
Total Fair Value	1
Total Unrealized Losses	$ 0