Invested Assets - Fair Value and Gross Unrealized Depreciation of Investments in Unrealized Loss Position (Detail) (USD $) In Millions, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Investment Holdings [Line Items]
Investment securities, Continuous unrealized loss position, Less Than 12 Months, Fair Value	$ 2,037	$ 8,089
Investment securities, Continuous unrealized loss position, Less Than 12 Months, Gross Unrealized Depreciation	24	262
Investment securities, Continuous unrealized loss position, 12 Months or More, Fair Value	2,748	692
Investment securities, Continuous unrealized loss position, 12 Months or More, Gross Unrealized Depreciation	64	66
Investment securities, Continuous unrealized loss position, Fair Value, Total	4,785	8,781
Investment securities, Continuous unrealized loss position, Gross Unrealized Depreciation, Total	88	328
Fixed Maturities [Member]
Investment Holdings [Line Items]
Investment securities, Continuous unrealized loss position, Less Than 12 Months, Fair Value	1,975	8,048
Investment securities, Continuous unrealized loss position, Less Than 12 Months, Gross Unrealized Depreciation	9	259
Investment securities, Continuous unrealized loss position, 12 Months or More, Fair Value	2,748	692
Investment securities, Continuous unrealized loss position, 12 Months or More, Gross Unrealized Depreciation	64	66
Investment securities, Continuous unrealized loss position, Fair Value, Total	4,723	8,740
Investment securities, Continuous unrealized loss position, Gross Unrealized Depreciation, Total	73	325
Equity Securities [Member]
Investment Holdings [Line Items]
Investment securities, Continuous unrealized loss position, Less Than 12 Months, Fair Value	62	41
Investment securities, Continuous unrealized loss position, Less Than 12 Months, Gross Unrealized Depreciation	15	3
Investment securities, Continuous unrealized loss position, Fair Value, Total	62	41
Investment securities, Continuous unrealized loss position, Gross Unrealized Depreciation, Total	15	3
Tax Exempt [Member] | Fixed Maturities [Member]
Investment Holdings [Line Items]
Investment securities, Continuous unrealized loss position, Less Than 12 Months, Fair Value	441	3,417
Investment securities, Continuous unrealized loss position, Less Than 12 Months, Gross Unrealized Depreciation	5	144
Investment securities, Continuous unrealized loss position, 12 Months or More, Fair Value	1,069	307
Investment securities, Continuous unrealized loss position, 12 Months or More, Gross Unrealized Depreciation	31	45
Investment securities, Continuous unrealized loss position, Fair Value, Total	1,510	3,724
Investment securities, Continuous unrealized loss position, Gross Unrealized Depreciation, Total	36	189
Taxable [Member] | Fixed Maturities [Member]
Investment Holdings [Line Items]
Investment securities, Continuous unrealized loss position, Less Than 12 Months, Fair Value	1,534	4,631
Investment securities, Continuous unrealized loss position, Less Than 12 Months, Gross Unrealized Depreciation	4	115
Investment securities, Continuous unrealized loss position, 12 Months or More, Fair Value	1,679	385
Investment securities, Continuous unrealized loss position, 12 Months or More, Gross Unrealized Depreciation	33	21
Investment securities, Continuous unrealized loss position, Fair Value, Total	3,213	5,016
Investment securities, Continuous unrealized loss position, Gross Unrealized Depreciation, Total	37	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	510	213
Investment securities, Continuous unrealized loss position, Less Than 12 Months, Gross Unrealized Depreciation		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	546	248
Investment securities, Continuous unrealized loss position, Gross Unrealized Depreciation, Total	2	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	502	2,526
Investment securities, Continuous unrealized loss position, Less Than 12 Months, Gross Unrealized Depreciation	2	76
Investment securities, Continuous unrealized loss position, 12 Months or More, Fair Value	1,097	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	1,599	2,748
Investment securities, Continuous unrealized loss position, Gross Unrealized Depreciation, Total	20	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	465	1,735
Investment securities, Continuous unrealized loss position, Less Than 12 Months, Gross Unrealized Depreciation	2	32
Investment securities, Continuous unrealized loss position, 12 Months or More, Fair Value	500	75
Investment securities, Continuous unrealized loss position, 12 Months or More, Gross Unrealized Depreciation	11	3
Investment securities, Continuous unrealized loss position, Fair Value, Total	965	1,810
Investment securities, Continuous unrealized loss position, Gross Unrealized Depreciation, Total	13	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	2	4
Investment securities, Continuous unrealized loss position, 12 Months or More, Fair Value	6	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	8	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	55	153
Investment securities, Continuous unrealized loss position, Less Than 12 Months, Gross Unrealized Depreciation		1
Investment securities, Continuous unrealized loss position, 12 Months or More, Fair Value	40	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	95	192
Investment securities, Continuous unrealized loss position, Gross Unrealized Depreciation, Total	$ 1	$ 3