Investments - Fair Values and Unrealized Losses by Investment Category and by Duration of Securities' Continuous Unrealized Loss Position (Detail) - USD ($) $ in Millions	Mar. 31, 2016	Dec. 31, 2015
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair Value	$ 1,294	$ 1,654
Less than 12 months Unrealized Losses	89	119
12 months or more Fair Value	178	284
12 months or more Unrealized Losses	24	37
Total Fair Value	1,472	1,938
Total Unrealized Losses	113	156
Fixed Maturities
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair Value	907	1,349
Less than 12 months Unrealized Losses	44	68
12 months or more Fair Value	178	284
12 months or more Unrealized Losses	24	37
Total Fair Value	1,085	1,633
Total Unrealized Losses	68	105
Fixed Maturities | Corporate
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair Value	801	1,099
Less than 12 months Unrealized Losses	43	63
12 months or more Fair Value	153	133
12 months or more Unrealized Losses	23	33
Total Fair Value	954	1,232
Total Unrealized Losses	66	96
Fixed Maturities | States, municipalities and political subdivisions
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair Value	28	47
Less than 12 months Unrealized Losses	0	1
12 months or more Fair Value	4	22
12 months or more Unrealized Losses	0	0
Total Fair Value	32	69
Total Unrealized Losses	0	1
Fixed Maturities | Commercial mortgage-backed
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair Value	49	103
Less than 12 months Unrealized Losses	1	2
12 months or more Fair Value	2	2
12 months or more Unrealized Losses	1	0
Total Fair Value	51	105
Total Unrealized Losses	2	2
Fixed Maturities | Government-sponsored enterprises
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair Value	29	100
Less than 12 months Unrealized Losses	0	2
12 months or more Fair Value	19	127
12 months or more Unrealized Losses	0	4
Total Fair Value	48	227
Total Unrealized Losses	0	6
Equity Securities
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair Value	387	305
Less than 12 months Unrealized Losses	45	51
12 months or more Fair Value	0	0
12 months or more Unrealized Losses	0	0
Total Fair Value	387	305
Total Unrealized Losses	45	51
Equity Securities | Common equities
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair Value	345	270
Less than 12 months Unrealized Losses	44	51
12 months or more Fair Value	0	0
12 months or more Unrealized Losses	0	0
Total Fair Value	345	270
Total Unrealized Losses	44	51
Equity Securities | Nonredeemable preferred equities
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair Value	42	35
Less than 12 months Unrealized Losses	1	0
12 months or more Fair Value	0	0
12 months or more Unrealized Losses	0	0
Total Fair Value	42	35
Total Unrealized Losses	$ 1	$ 0