Fair Value - Quantitative Information about Significant Unobservable Inputs Utilized by Company Fair Value in Measurements of Level 3 Assets (Detail) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014
Fixed Maturity Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Credit spread adjustment	3.00%	3.00%
Fixed Maturity Securities [Member] | Discounted Cash Flow [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value Assets	102		$ 101
Valuation Techniques	Discounted cash flow
Fixed Maturity Securities [Member] | Minimum [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Credit spread adjustment	2.00%	2.00%
Fixed Maturity Securities [Member] | Maximum [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Credit spread adjustment	13.00%	13.00%
Equity Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Private offering price	682	600
Equity Securities [Member] | Market approach [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value Assets	13		16
Valuation Techniques	Market approach
Equity Securities [Member] | Minimum [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Private offering price	10	12
Equity Securities [Member] | Maximum [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Private offering price	4,400	4,391
Life Settlement Contracts [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Discount rate risk premium	9.00%	9.00%
Mortality assumption	164.00%	163.00%
Life Settlement Contracts [Member] | Discounted Cash Flow [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value Assets	79		$ 82
Valuation Techniques	Discounted cash flow
Life Settlement Contracts [Member] | Minimum [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Mortality assumption	55.00%	55.00%
Life Settlement Contracts [Member] | Maximum [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Mortality assumption	1676.00%	1676.00%