Invested Assets and Related Income - Amortized Cost and Fair Value of Fixed Maturities and Equity Securities (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Investment Holdings [Line Items]
Fixed maturities, Amortized Cost	$ 36,958	$ 35,959
Fixed maturities, Gross Unrealized Appreciation	1,884	1,457
Fixed maturities, Gross Unrealized Depreciation	62	325
Fixed maturities, Fair Value	38,780	37,091
Equity securities, Amortized Cost	1,089	1,057
Equity securities, Gross Unrealized Appreciation	894	756
Equity securities, Gross Unrealized Depreciation	19	3
Equity securities, Fair Value	1,964	1,810
Tax Exempt [Member]
Investment Holdings [Line Items]
Fixed maturities, Amortized Cost	18,614	17,808
Fixed maturities, Gross Unrealized Appreciation	1,174	802
Fixed maturities, Gross Unrealized Depreciation	16	189
Fixed maturities, Fair Value	19,772	18,421
Taxable [Member]
Investment Holdings [Line Items]
Fixed maturities, Amortized Cost	18,344	18,151
Fixed maturities, Gross Unrealized Appreciation	710	655
Fixed maturities, Gross Unrealized Depreciation	46	136
Fixed maturities, Fair Value	19,008	18,670
Taxable [Member] \| Residential Mortgage-backed Securities [Member]
Investment Holdings [Line Items]
Fixed maturities, Amortized Cost	192	277
Fixed maturities, Gross Unrealized Appreciation	20	23
Fixed maturities, Gross Unrealized Depreciation	1	1
Fixed maturities, Fair Value	211	299
Taxable [Member] \| Commercial Mortgage-backed Securities [Member]
Investment Holdings [Line Items]
Fixed maturities, Amortized Cost	1,069	1,339
Fixed maturities, Gross Unrealized Appreciation	22	29
Fixed maturities, Gross Unrealized Depreciation	1	3
Fixed maturities, Fair Value	1,090	1,365
Taxable [Member] \| U.S. Government and Government Agency and Authority Obligations [Member]
Investment Holdings [Line Items]
Fixed maturities, Amortized Cost	1,962	784
Fixed maturities, Gross Unrealized Appreciation	46	27
Fixed maturities, Gross Unrealized Depreciation	1	9
Fixed maturities, Fair Value	2,007	802
Taxable [Member] \| Corporate Bonds [Member]
Investment Holdings [Line Items]
Fixed maturities, Amortized Cost	8,741	9,032
Fixed maturities, Gross Unrealized Appreciation	327	370
Fixed maturities, Gross Unrealized Depreciation	40	88
Fixed maturities, Fair Value	9,028	9,314
Taxable [Member] \| Foreign Government and Government Agency Obligations [Member]
Investment Holdings [Line Items]
Fixed maturities, Amortized Cost	6,380	6,719
Fixed maturities, Gross Unrealized Appreciation	295	206
Fixed maturities, Gross Unrealized Depreciation	3	35
Fixed maturities, Fair Value	$ 6,672	$ 6,890

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

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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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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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