Invested Assets - Amortized Cost and Fair Value of Fixed Maturities and Equity Securities (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Investment Holdings [Line Items]
Fixed maturities, Amortized Cost	$ 36,483	$ 36,958
Fixed maturities, Gross Unrealized Appreciation	2,022	1,884
Fixed maturities, Gross Unrealized Depreciation	48	62
Fixed maturities, Fair Value	38,457	38,780
Equity securities, Amortized Cost	1,074	1,089
Equity securities, Gross Unrealized Appreciation	900	894
Equity securities, Gross Unrealized Depreciation	10	19
Equity securities, Fair Value	1,964	1,964
Tax Exempt [Member]
Investment Holdings [Line Items]
Fixed maturities, Amortized Cost	19,260	18,614
Fixed maturities, Gross Unrealized Appreciation	1,179	1,174
Fixed maturities, Gross Unrealized Depreciation	24	16
Fixed maturities, Fair Value	20,415	19,772
Taxable [Member]
Investment Holdings [Line Items]
Fixed maturities, Amortized Cost	17,223	18,344
Fixed maturities, Gross Unrealized Appreciation	843	710
Fixed maturities, Gross Unrealized Depreciation	24	46
Fixed maturities, Fair Value	18,042	19,008
Taxable [Member] \| Residential Mortgage-backed Securities [Member]
Investment Holdings [Line Items]
Fixed maturities, Amortized Cost	175	192
Fixed maturities, Gross Unrealized Appreciation	20	20
Fixed maturities, Gross Unrealized Depreciation	1	1
Fixed maturities, Fair Value	194	211
Taxable [Member] \| Commercial Mortgage-backed Securities [Member]
Investment Holdings [Line Items]
Fixed maturities, Amortized Cost	988	1,069
Fixed maturities, Gross Unrealized Appreciation	27	22
Fixed maturities, Gross Unrealized Depreciation	1	1
Fixed maturities, Fair Value	1,014	1,090
Taxable [Member] \| U.S. Government and Government Agency and Authority Obligations [Member]
Investment Holdings [Line Items]
Fixed maturities, Amortized Cost	1,460	1,962
Fixed maturities, Gross Unrealized Appreciation	59	46
Fixed maturities, Gross Unrealized Depreciation	1	1
Fixed maturities, Fair Value	1,518	2,007
Taxable [Member] \| Corporate Bonds [Member]
Investment Holdings [Line Items]
Fixed maturities, Amortized Cost	8,756	8,741
Fixed maturities, Gross Unrealized Appreciation	402	327
Fixed maturities, Gross Unrealized Depreciation	19	40
Fixed maturities, Fair Value	9,139	9,028
Taxable [Member] \| Foreign Government and Government Agency Obligations [Member]
Investment Holdings [Line Items]
Fixed maturities, Amortized Cost	5,844	6,380
Fixed maturities, Gross Unrealized Appreciation	335	295
Fixed maturities, Gross Unrealized Depreciation	2	3
Fixed maturities, Fair Value	$ 6,177	$ 6,672

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

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (b)

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

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This item represents the cost of debt securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any.

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-Publisher FASB

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

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Amount of debt securities categorized neither as held-to-maturity nor trading.

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Amount of equity securities categorized neither as held-to-maturity nor as trading.

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