Invested Assets - Fair Value and Gross Unrealized Depreciation of Investments in Unrealized Loss Position (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Investment Holdings [Line Items]
Investment securities, Continuous unrealized loss position, Less Than 12 Months, Fair Value	$ 2,762	$ 8,089
Investment securities, Continuous unrealized loss position, Less Than 12 Months, Gross Unrealized Depreciation	29	262
Investment securities, Continuous unrealized loss position, 12 Months or More, Fair Value	2,072	692
Investment securities, Continuous unrealized loss position, 12 Months or More, Gross Unrealized Depreciation	50	66
Investment securities, Continuous unrealized loss position, Fair Value, Total	4,834	8,781
Investment securities, Continuous unrealized loss position, Gross Unrealized Depreciation, Total	79	328
Fixed Maturities [Member]
Investment Holdings [Line Items]
Investment securities, Continuous unrealized loss position, Less Than 12 Months, Fair Value	2,663	8,048
Investment securities, Continuous unrealized loss position, Less Than 12 Months, Gross Unrealized Depreciation	15	259
Investment securities, Continuous unrealized loss position, 12 Months or More, Fair Value	2,072	692
Investment securities, Continuous unrealized loss position, 12 Months or More, Gross Unrealized Depreciation	50	66
Investment securities, Continuous unrealized loss position, Fair Value, Total	4,735	8,740
Investment securities, Continuous unrealized loss position, Gross Unrealized Depreciation, Total	65	325
Equity Securities [Member]
Investment Holdings [Line Items]
Investment securities, Continuous unrealized loss position, Less Than 12 Months, Fair Value	99	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	99	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	366	3,417
Investment securities, Continuous unrealized loss position, Less Than 12 Months, Gross Unrealized Depreciation	2	144
Investment securities, Continuous unrealized loss position, 12 Months or More, Fair Value	449	307
Investment securities, Continuous unrealized loss position, 12 Months or More, Gross Unrealized Depreciation	16	45
Investment securities, Continuous unrealized loss position, Fair Value, Total	815	3,724
Investment securities, Continuous unrealized loss position, Gross Unrealized Depreciation, Total	18	189
Taxable [Member] | Fixed Maturities [Member]
Investment Holdings [Line Items]
Investment securities, Continuous unrealized loss position, Less Than 12 Months, Fair Value	2,297	4,631
Investment securities, Continuous unrealized loss position, Less Than 12 Months, Gross Unrealized Depreciation	13	115
Investment securities, Continuous unrealized loss position, 12 Months or More, Fair Value	1,623	385
Investment securities, Continuous unrealized loss position, 12 Months or More, Gross Unrealized Depreciation	34	21
Investment securities, Continuous unrealized loss position, Fair Value, Total	3,920	5,016
Investment securities, Continuous unrealized loss position, Gross Unrealized Depreciation, Total	47	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	616	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	35	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	651	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	1,193	2,526
Investment securities, Continuous unrealized loss position, Less Than 12 Months, Gross Unrealized Depreciation	11	76
Investment securities, Continuous unrealized loss position, 12 Months or More, Fair Value	1,062	222
Investment securities, Continuous unrealized loss position, 12 Months or More, Gross Unrealized Depreciation	24	12
Investment securities, Continuous unrealized loss position, Fair Value, Total	2,255	2,748
Investment securities, Continuous unrealized loss position, Gross Unrealized Depreciation, Total	35	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	364	1,735
Investment securities, Continuous unrealized loss position, Less Than 12 Months, Gross Unrealized Depreciation	1	32
Investment securities, Continuous unrealized loss position, 12 Months or More, Fair Value	479	75
Investment securities, Continuous unrealized loss position, 12 Months or More, Gross Unrealized Depreciation	6	3
Investment securities, Continuous unrealized loss position, Fair Value, Total	843	1,810
Investment securities, Continuous unrealized loss position, Gross Unrealized Depreciation, Total	7	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, Less Than 12 Months, Gross Unrealized Depreciation
Investment securities, Continuous unrealized loss position, 12 Months or More, Fair Value	5	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	7	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	122	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	42	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	164	192
Investment securities, Continuous unrealized loss position, Gross Unrealized Depreciation, Total	$ 2	$ 3