Invested Assets - Amortized Cost and Fair Value of Fixed Maturities and Equity Securities (Detail) - USD ($) $ in Millions	Jun. 30, 2015	Dec. 31, 2014
Investment Holdings [Line Items]
Fixed maturities, Amortized Cost	$ 36,467	$ 36,958
Fixed maturities, Gross Unrealized Appreciation	1,538	1,884
Fixed maturities, Gross Unrealized Depreciation	125	62
Fixed maturities, Fair Value	37,880	38,780
Equity securities, Amortized Cost	1,083	1,089
Equity securities, Gross Unrealized Appreciation	887	894
Equity securities, Gross Unrealized Depreciation	13	19
Equity securities, Fair Value	1,957	1,964
Tax Exempt [Member]
Investment Holdings [Line Items]
Fixed maturities, Amortized Cost	19,433	18,614
Fixed maturities, Gross Unrealized Appreciation	890	1,174
Fixed maturities, Gross Unrealized Depreciation	79	16
Fixed maturities, Fair Value	20,244	19,772
Taxable [Member]
Investment Holdings [Line Items]
Fixed maturities, Amortized Cost	17,034	18,344
Fixed maturities, Gross Unrealized Appreciation	648	710
Fixed maturities, Gross Unrealized Depreciation	46	46
Fixed maturities, Fair Value	17,636	19,008
Taxable [Member] \| Residential Mortgage-backed Securities [Member]
Investment Holdings [Line Items]
Fixed maturities, Amortized Cost	158	192
Fixed maturities, Gross Unrealized Appreciation	17	20
Fixed maturities, Gross Unrealized Depreciation	1	1
Fixed maturities, Fair Value	174	211
Taxable [Member] \| Commercial Mortgage-backed Securities [Member]
Investment Holdings [Line Items]
Fixed maturities, Amortized Cost	971	1,069
Fixed maturities, Gross Unrealized Appreciation	19	22
Fixed maturities, Gross Unrealized Depreciation	1	1
Fixed maturities, Fair Value	989	1,090
Taxable [Member] \| U.S. Government and Government Agency and Authority Obligations [Member]
Investment Holdings [Line Items]
Fixed maturities, Amortized Cost	1,241	1,962
Fixed maturities, Gross Unrealized Appreciation	41	46
Fixed maturities, Gross Unrealized Depreciation	3	1
Fixed maturities, Fair Value	1,279	2,007
Taxable [Member] \| Corporate Bonds [Member]
Investment Holdings [Line Items]
Fixed maturities, Amortized Cost	8,723	8,741
Fixed maturities, Gross Unrealized Appreciation	284	327
Fixed maturities, Gross Unrealized Depreciation	34	40
Fixed maturities, Fair Value	8,973	9,028
Taxable [Member] \| Foreign Government and Government Agency Obligations [Member]
Investment Holdings [Line Items]
Fixed maturities, Amortized Cost	5,941	6,380
Fixed maturities, Gross Unrealized Appreciation	287	295
Fixed maturities, Gross Unrealized Depreciation	7	3
Fixed maturities, Fair Value	$ 6,221	$ 6,672

Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in debt securities classified as available-for-sale.

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