Invested Assets - Fair Value and Gross Unrealized Depreciation of Investments in Unrealized Loss Position (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Investment Holdings [Line Items]
Investment securities, Continuous unrealized loss position, Less Than 12 Months, Fair Value	$ 4,579	$ 8,089
Investment securities, Continuous unrealized loss position, Less Than 12 Months, Gross Unrealized Depreciation	91	262
Investment securities, Continuous unrealized loss position, 12 Months or More, Fair Value	1,507	692
Investment securities, Continuous unrealized loss position, 12 Months or More, Gross Unrealized Depreciation	79	66
Investment securities, Continuous unrealized loss position, Fair Value, Total	6,086	8,781
Investment securities, Continuous unrealized loss position, Gross Unrealized Depreciation, Total	170	328
Fixed Maturities [Member]
Investment Holdings [Line Items]
Investment securities, Continuous unrealized loss position, Less Than 12 Months, Fair Value	4,477	8,048
Investment securities, Continuous unrealized loss position, Less Than 12 Months, Gross Unrealized Depreciation	77	259
Investment securities, Continuous unrealized loss position, 12 Months or More, Fair Value	1,507	692
Investment securities, Continuous unrealized loss position, 12 Months or More, Gross Unrealized Depreciation	79	66
Investment securities, Continuous unrealized loss position, Fair Value, Total	5,984	8,740
Investment securities, Continuous unrealized loss position, Gross Unrealized Depreciation, Total	156	325
Equity Securities [Member]
Investment Holdings [Line Items]
Investment securities, Continuous unrealized loss position, Less Than 12 Months, Fair Value	102	41
Investment securities, Continuous unrealized loss position, Less Than 12 Months, Gross Unrealized Depreciation	14	3
Investment securities, Continuous unrealized loss position, 12 Months or More, Fair Value
Investment securities, Continuous unrealized loss position, 12 Months or More, Gross Unrealized Depreciation
Investment securities, Continuous unrealized loss position, Fair Value, Total	102	41
Investment securities, Continuous unrealized loss position, Gross Unrealized Depreciation, Total	14	3
Tax Exempt [Member] | Fixed Maturities [Member]
Investment Holdings [Line Items]
Investment securities, Continuous unrealized loss position, Less Than 12 Months, Fair Value	1,540	3,417
Investment securities, Continuous unrealized loss position, Less Than 12 Months, Gross Unrealized Depreciation	32	144
Investment securities, Continuous unrealized loss position, 12 Months or More, Fair Value	819	307
Investment securities, Continuous unrealized loss position, 12 Months or More, Gross Unrealized Depreciation	52	45
Investment securities, Continuous unrealized loss position, Fair Value, Total	2,359	3,724
Investment securities, Continuous unrealized loss position, Gross Unrealized Depreciation, Total	84	189
Taxable [Member] | Fixed Maturities [Member]
Investment Holdings [Line Items]
Investment securities, Continuous unrealized loss position, Less Than 12 Months, Fair Value	2,937	4,631
Investment securities, Continuous unrealized loss position, Less Than 12 Months, Gross Unrealized Depreciation	45	115
Investment securities, Continuous unrealized loss position, 12 Months or More, Fair Value	688	385
Investment securities, Continuous unrealized loss position, 12 Months or More, Gross Unrealized Depreciation	27	21
Investment securities, Continuous unrealized loss position, Fair Value, Total	3,625	5,016
Investment securities, Continuous unrealized loss position, Gross Unrealized Depreciation, Total	72	136
Taxable [Member] | U.S. Government and Government Agency and Authority Obligations [Member] | Fixed Maturities [Member]
Investment Holdings [Line Items]
Investment securities, Continuous unrealized loss position, Less Than 12 Months, Fair Value	128	213
Investment securities, Continuous unrealized loss position, Less Than 12 Months, Gross Unrealized Depreciation	1	6
Investment securities, Continuous unrealized loss position, 12 Months or More, Fair Value	36	35
Investment securities, Continuous unrealized loss position, 12 Months or More, Gross Unrealized Depreciation	2	3
Investment securities, Continuous unrealized loss position, Fair Value, Total	164	248
Investment securities, Continuous unrealized loss position, Gross Unrealized Depreciation, Total	3	9
Taxable [Member] | Corporate Bonds [Member] | Fixed Maturities [Member]
Investment Holdings [Line Items]
Investment securities, Continuous unrealized loss position, Less Than 12 Months, Fair Value	1,534	2,526
Investment securities, Continuous unrealized loss position, Less Than 12 Months, Gross Unrealized Depreciation	29	76
Investment securities, Continuous unrealized loss position, 12 Months or More, Fair Value	462	222
Investment securities, Continuous unrealized loss position, 12 Months or More, Gross Unrealized Depreciation	18	12
Investment securities, Continuous unrealized loss position, Fair Value, Total	1,996	2,748
Investment securities, Continuous unrealized loss position, Gross Unrealized Depreciation, Total	47	88
Taxable [Member] | Foreign Government and Government Agency Obligations [Member] | Fixed Maturities [Member]
Investment Holdings [Line Items]
Investment securities, Continuous unrealized loss position, Less Than 12 Months, Fair Value	1,096	1,735
Investment securities, Continuous unrealized loss position, Less Than 12 Months, Gross Unrealized Depreciation	14	32
Investment securities, Continuous unrealized loss position, 12 Months or More, Fair Value	147	75
Investment securities, Continuous unrealized loss position, 12 Months or More, Gross Unrealized Depreciation	5	3
Investment securities, Continuous unrealized loss position, Fair Value, Total	1,243	1,810
Investment securities, Continuous unrealized loss position, Gross Unrealized Depreciation, Total	19	35
Residential Mortgage-backed Securities [Member] | Taxable [Member] | Fixed Maturities [Member]
Investment Holdings [Line Items]
Investment securities, Continuous unrealized loss position, Less Than 12 Months, Fair Value	3	4
Investment securities, Continuous unrealized loss position, Less Than 12 Months, Gross Unrealized Depreciation
Investment securities, Continuous unrealized loss position, 12 Months or More, Fair Value	9	14
Investment securities, Continuous unrealized loss position, 12 Months or More, Gross Unrealized Depreciation	1	1
Investment securities, Continuous unrealized loss position, Fair Value, Total	12	18
Investment securities, Continuous unrealized loss position, Gross Unrealized Depreciation, Total	1	1
Commercial Mortgage-backed Securities [Member] | Taxable [Member] | Fixed Maturities [Member]
Investment Holdings [Line Items]
Investment securities, Continuous unrealized loss position, Less Than 12 Months, Fair Value	176	153
Investment securities, Continuous unrealized loss position, Less Than 12 Months, Gross Unrealized Depreciation	1	1
Investment securities, Continuous unrealized loss position, 12 Months or More, Fair Value	34	39
Investment securities, Continuous unrealized loss position, 12 Months or More, Gross Unrealized Depreciation	1	2
Investment securities, Continuous unrealized loss position, Fair Value, Total	210	192
Investment securities, Continuous unrealized loss position, Gross Unrealized Depreciation, Total	$ 2	$ 3