Investments - Fair Values and Unrealized Losses by Investment Category and by Duration of Securities' Continuous Unrealized Loss Position (Detail) (USD $) In Millions, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair Value	$ 164	$ 1,516
Less than 12 months Unrealized Losses	1	74
12 months or more Fair Value	708	86
12 months or more Unrealized Losses	25	5
Total Fair Value	872	1,602
Total Unrealized Losses	26	79
Fixed Maturities
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair Value	120	1,397
Less than 12 months Unrealized Losses	1	70
12 months or more Fair Value	612	86
12 months or more Unrealized Losses	21	5
Total Fair Value	732	1,483
Total Unrealized Losses	22	75
Fixed Maturities | States, Municipalities And Political Subdivisions
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair Value	61	490
Less than 12 months Unrealized Losses	1	18
12 months or more Fair Value	267	42
12 months or more Unrealized Losses	4	3
Total Fair Value	328	532
Total Unrealized Losses	5	21
Fixed Maturities | United States Government
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair Value	0	1
Less than 12 months Unrealized Losses	0	0
12 months or more Fair Value	1	0
12 months or more Unrealized Losses	0	0
Total Fair Value	1	1
Total Unrealized Losses	0	0
Fixed Maturities | Government-Sponsored Enterprises
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair Value	10	199
Less than 12 months Unrealized Losses	0	27
12 months or more Fair Value	175	1
12 months or more Unrealized Losses	13	0
Total Fair Value	185	200
Total Unrealized Losses	13	27
Fixed Maturities | Foreign Government Debt Securities [Member]
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair Value	0	10
Less than 12 months Unrealized Losses	0	0
12 months or more Fair Value	10	0
12 months or more Unrealized Losses	0	0
Total Fair Value	10	10
Total Unrealized Losses	0	0
Fixed Maturities | Commercial Mortgage Backed Securities
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair Value	0	125
Less than 12 months Unrealized Losses	0	5
12 months or more Fair Value	32	0
12 months or more Unrealized Losses	1	0
Total Fair Value	32	125
Total Unrealized Losses	1	5
Fixed Maturities | Corporate Securities
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair Value	49	572
Less than 12 months Unrealized Losses	0	20
12 months or more Fair Value	127	43
12 months or more Unrealized Losses	3	2
Total Fair Value	176	615
Total Unrealized Losses	3	22
Equity Securities
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair Value	44	119
Less than 12 months Unrealized Losses	0	4
12 months or more Fair Value	96	0
12 months or more Unrealized Losses	4	0
Total Fair Value	140	119
Total Unrealized Losses	4	4
Equity Securities | Common Stock
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair Value	39	77
Less than 12 months Unrealized Losses	0	1
12 months or more Fair Value	79	0
12 months or more Unrealized Losses	3	0
Total Fair Value	118	77
Total Unrealized Losses	3	1
Equity Securities | Preferred Stock
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair Value	5	42
Less than 12 months Unrealized Losses	0	3
12 months or more Fair Value	17	0
12 months or more Unrealized Losses	1	0
Total Fair Value	22	42
Total Unrealized Losses	$ 1	$ 3