Invested Assets and Related Income - Fair Value and Gross Unrealized Depreciation of Investments in Unrealized Loss Position (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Investment Holdings [Line Items]
Investment securities, Continuous unrealized loss position, Less Than 12 Months, Fair Value	$ 8,089	$ 1,378
Investment securities, Continuous unrealized loss position, Less Than 12 Months, Gross Unrealized Depreciation	262	31
Investment securities, Continuous unrealized loss position, 12 Months or More, Fair Value	692	236
Investment securities, Continuous unrealized loss position, 12 Months or More, Gross Unrealized Depreciation	66	29
Investment securities, Continuous unrealized loss position, Fair Value, Total	8,781	1,614
Investment securities, Continuous unrealized loss position, Gross Unrealized Depreciation, Total	328	60
Fixed Maturities [Member]
Investment Holdings [Line Items]
Investment securities, Continuous unrealized loss position, Less Than 12 Months, Fair Value	8,048	1,196
Investment securities, Continuous unrealized loss position, Less Than 12 Months, Gross Unrealized Depreciation	259	10
Investment securities, Continuous unrealized loss position, 12 Months or More, Fair Value	692	173
Investment securities, Continuous unrealized loss position, 12 Months or More, Gross Unrealized Depreciation	66	16
Investment securities, Continuous unrealized loss position, Fair Value, Total	8,740	1,369
Investment securities, Continuous unrealized loss position, Gross Unrealized Depreciation, Total	325	26
Equity Securities [Member]
Investment Holdings [Line Items]
Investment securities, Continuous unrealized loss position, Less Than 12 Months, Fair Value	41	182
Investment securities, Continuous unrealized loss position, Less Than 12 Months, Gross Unrealized Depreciation	3	21
Investment securities, Continuous unrealized loss position, 12 Months or More, Fair Value		63
Investment securities, Continuous unrealized loss position, 12 Months or More, Gross Unrealized Depreciation		13
Investment securities, Continuous unrealized loss position, Fair Value, Total	41	245
Investment securities, Continuous unrealized loss position, Gross Unrealized Depreciation, Total	3	34
Tax Exempt [Member] | Fixed Maturities [Member]
Investment Holdings [Line Items]
Investment securities, Continuous unrealized loss position, Less Than 12 Months, Fair Value	3,417	344
Investment securities, Continuous unrealized loss position, Less Than 12 Months, Gross Unrealized Depreciation	144	6
Investment securities, Continuous unrealized loss position, 12 Months or More, Fair Value	307	104
Investment securities, Continuous unrealized loss position, 12 Months or More, Gross Unrealized Depreciation	45	13
Investment securities, Continuous unrealized loss position, Fair Value, Total	3,724	448
Investment securities, Continuous unrealized loss position, Gross Unrealized Depreciation, Total	189	19
Taxable [Member] | Fixed Maturities [Member]
Investment Holdings [Line Items]
Investment securities, Continuous unrealized loss position, Less Than 12 Months, Fair Value	4,631	852
Investment securities, Continuous unrealized loss position, Less Than 12 Months, Gross Unrealized Depreciation	115	4
Investment securities, Continuous unrealized loss position, 12 Months or More, Fair Value	385	69
Investment securities, Continuous unrealized loss position, 12 Months or More, Gross Unrealized Depreciation	21	3
Investment securities, Continuous unrealized loss position, Fair Value, Total	5,016	921
Investment securities, Continuous unrealized loss position, Gross Unrealized Depreciation, Total	136	7
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	213	28
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	20
Investment securities, Continuous unrealized loss position, 12 Months or More, Gross Unrealized Depreciation	3
Investment securities, Continuous unrealized loss position, Fair Value, Total	248	48
Investment securities, Continuous unrealized loss position, Gross Unrealized Depreciation, Total	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	2,526	289
Investment securities, Continuous unrealized loss position, Less Than 12 Months, Gross Unrealized Depreciation	76	2
Investment securities, Continuous unrealized loss position, 12 Months or More, Fair Value	222	14
Investment securities, Continuous unrealized loss position, 12 Months or More, Gross Unrealized Depreciation	12	1
Investment securities, Continuous unrealized loss position, Fair Value, Total	2,748	303
Investment securities, Continuous unrealized loss position, Gross Unrealized Depreciation, Total	88	3
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	1,735	429
Investment securities, Continuous unrealized loss position, Less Than 12 Months, Gross Unrealized Depreciation	32	1
Investment securities, Continuous unrealized loss position, 12 Months or More, Fair Value	75	13
Investment securities, Continuous unrealized loss position, 12 Months or More, Gross Unrealized Depreciation	3
Investment securities, Continuous unrealized loss position, Fair Value, Total	1,810	442
Investment securities, Continuous unrealized loss position, Gross Unrealized Depreciation, Total	35	1
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	4	1
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	14	19
Investment securities, Continuous unrealized loss position, 12 Months or More, Gross Unrealized Depreciation	1	2
Investment securities, Continuous unrealized loss position, Fair Value, Total	18	20
Investment securities, Continuous unrealized loss position, Gross Unrealized Depreciation, Total	1	2
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	153	105
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	39	3
Investment securities, Continuous unrealized loss position, 12 Months or More, Gross Unrealized Depreciation	2
Investment securities, Continuous unrealized loss position, Fair Value, Total	192	108
Investment securities, Continuous unrealized loss position, Gross Unrealized Depreciation, Total	$ 3	$ 1