Investments - Fair Values and Unrealized Losses by Investment Category and by Duration of Securities' Continuous Unrealized Loss Position (Detail) (USD $)	Mar. 31, 2014	Dec. 31, 2013
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair Value	$ 840,000,000	$ 1,516,000,000
Less than 12 months Unrealized Losses	30,000,000	74,000,000
12 months or more Fair Value	274,000,000	86,000,000
12 months or more Unrealized Losses	19,000,000	5,000,000
Total Fair Value	1,114,000,000	1,602,000,000
Total Unrealized Losses	49,000,000	79,000,000
Fixed Maturities
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair Value	729,000,000	1,397,000,000
Less than 12 months Unrealized Losses	23,000,000	70,000,000
12 months or more Fair Value	274,000,000	86,000,000
12 months or more Unrealized Losses	19,000,000	5,000,000
Total Fair Value	1,003,000,000	1,483,000,000
Total Unrealized Losses	42,000,000	75,000,000
Fixed Maturities | States, Municipalities And Political Subdivisions
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair Value	289,000,000	490,000,000
Less than 12 months Unrealized Losses	7,000,000	18,000,000
12 months or more Fair Value	98,000,000	42,000,000
12 months or more Unrealized Losses	5,000,000	3,000,000
Total Fair Value	387,000,000	532,000,000
Total Unrealized Losses	12,000,000	21,000,000
Fixed Maturities | United States Government
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair Value	11,000,000	1,000,000
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	11,000,000	1,000,000
Total Unrealized Losses	0	0
Fixed Maturities | Government-Sponsored Enterprises
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair Value	83,000,000	199,000,000
Less than 12 months Unrealized Losses	8,000,000	27,000,000
12 months or more Fair Value	96,000,000	1,000,000
12 months or more Unrealized Losses	12,000,000	0
Total Fair Value	179,000,000	200,000,000
Total Unrealized Losses	20,000,000	27,000,000
Fixed Maturities | Commercial Mortgage Backed Securities
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair Value	55,000,000
Less than 12 months Unrealized Losses	1,000,000
12 months or more Fair Value	15,000,000
12 months or more Unrealized Losses	1,000,000
Total Fair Value	70,000,000
Total Unrealized Losses	2,000,000
Fixed Maturities | Corporate Securities
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair Value	291,000,000	572,000,000
Less than 12 months Unrealized Losses	7,000,000	20,000,000
12 months or more Fair Value	65,000,000	43,000,000
12 months or more Unrealized Losses	1,000,000	2,000,000
Total Fair Value	356,000,000	615,000,000
Total Unrealized Losses	8,000,000	22,000,000
Equity Securities
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair Value	111,000,000	119,000,000
Less than 12 months Unrealized Losses	7,000,000	4,000,000
12 months or more Fair Value	0	0
12 months or more Unrealized Losses	500,000,000	0
Total Fair Value	111,000,000	119,000,000
Total Unrealized Losses	7,000,000	4,000,000
Equity Securities | Common Stock
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair Value	72,000,000	77,000,000
Less than 12 months Unrealized Losses	6,000,000	1,000,000
12 months or more Fair Value	0
Total Fair Value	72,000,000	77,000,000
Total Unrealized Losses	6,000,000	1,000,000
Equity Securities | Preferred Stock
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair Value	39,000,000	42,000,000
Less than 12 months Unrealized Losses	1,000,000	3,000,000
12 months or more Fair Value	0	0
12 months or more Unrealized Losses		0
Total Fair Value	39,000,000	42,000,000
Total Unrealized Losses	$ 1,000,000	$ 3,000,000