Invested Assets - Amortized Cost and Fair Value of Fixed Maturities and Equity Securities (Detail) - USD ($) $ in Millions	Sep. 30, 2015	Dec. 31, 2014
Investment Holdings [Line Items]
Fixed maturities, Amortized Cost	$ 35,469	$ 36,958
Fixed maturities, Gross Unrealized Appreciation	1,629	1,884
Fixed maturities, Gross Unrealized Depreciation	82	62
Fixed maturities, Fair Value	37,016	38,780
Equity securities, Amortized Cost	1,060	1,089
Equity securities, Gross Unrealized Appreciation	742	894
Equity securities, Gross Unrealized Depreciation	31	19
Equity securities, Fair Value	1,771	1,964
Tax Exempt [Member]
Investment Holdings [Line Items]
Fixed maturities, Amortized Cost	18,890	18,614
Fixed maturities, Gross Unrealized Appreciation	1,012	1,174
Fixed maturities, Gross Unrealized Depreciation	29	16
Fixed maturities, Fair Value	19,873	19,772
Taxable [Member]
Investment Holdings [Line Items]
Fixed maturities, Amortized Cost	16,579	18,344
Fixed maturities, Gross Unrealized Appreciation	617	710
Fixed maturities, Gross Unrealized Depreciation	53	46
Fixed maturities, Fair Value	17,143	19,008
Taxable [Member] \| Residential Mortgage-backed Securities [Member]
Investment Holdings [Line Items]
Fixed maturities, Amortized Cost	110	192
Fixed maturities, Gross Unrealized Appreciation	15	20
Fixed maturities, Gross Unrealized Depreciation	1	1
Fixed maturities, Fair Value	124	211
Taxable [Member] \| Commercial Mortgage-backed Securities [Member]
Investment Holdings [Line Items]
Fixed maturities, Amortized Cost	943	1,069
Fixed maturities, Gross Unrealized Appreciation	19	22
Fixed maturities, Gross Unrealized Depreciation	1	1
Fixed maturities, Fair Value	961	1,090
Taxable [Member] \| U.S. Government and Government Agency and Authority Obligations [Member]
Investment Holdings [Line Items]
Fixed maturities, Amortized Cost	1,259	1,962
Fixed maturities, Gross Unrealized Appreciation	54	46
Fixed maturities, Gross Unrealized Depreciation	1	1
Fixed maturities, Fair Value	1,312	2,007
Taxable [Member] \| Corporate Bonds [Member]
Investment Holdings [Line Items]
Fixed maturities, Amortized Cost	8,409	8,741
Fixed maturities, Gross Unrealized Appreciation	260	327
Fixed maturities, Gross Unrealized Depreciation	45	40
Fixed maturities, Fair Value	8,624	9,028
Taxable [Member] \| Foreign Government and Government Agency Obligations [Member]
Investment Holdings [Line Items]
Fixed maturities, Amortized Cost	5,858	6,380
Fixed maturities, Gross Unrealized Appreciation	269	295
Fixed maturities, Gross Unrealized Depreciation	5	3
Fixed maturities, Fair Value	$ 6,122	$ 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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