Investments - Realized Investment Gains and Losses and Change in Unrealized Investment Gains and Losses and Other Items (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
Mar. 31, 2015	Mar. 31, 2014
Investment income summary:
Interest	$ 105us-gaap_InvestmentIncomeInterest	$ 104us-gaap_InvestmentIncomeInterest
Dividends	36us-gaap_InvestmentIncomeDividend	32us-gaap_InvestmentIncomeDividend
Other	0	1
Total	141us-gaap_GrossInvestmentIncomeOperating	137us-gaap_GrossInvestmentIncomeOperating
Less investment expenses	2	2
Total	139us-gaap_NetInvestmentIncome	135us-gaap_NetInvestmentIncome
Realized investment gains and losses summary:
Realized investment gains, net	47us-gaap_RealizedInvestmentGainsLosses	22us-gaap_RealizedInvestmentGainsLosses
Change in unrealized gains and losses summary:
Fixed maturities	(28)	76
Less income taxes	(15)us-gaap_OtherComprehensiveIncomeLossTax	41us-gaap_OtherComprehensiveIncomeLossTax
Other comprehensive income (loss), net of tax	(28)	74
Fixed Maturities
Realized investment gains and losses summary:
Gross realized gains	3	2
Gross realized losses	0	(1)
Other-than-temporary impairments	0	0
Change in unrealized gains and losses summary:
Fixed maturities	46	88
Equity Securities
Realized investment gains and losses summary:
Gross realized gains	44	18
Gross realized losses	(1)	0
Other-than-temporary impairments	0	(1)
Other	1	4
Change in unrealized gains and losses summary:
Fixed maturities	$ (89)	$ 29

Income derived from those other than interest and dividends.

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This item represents realized investment gains (losses) included in earnings for the period excluding those relating to other than temporary impairment losses on investments in debt securities. Includes realized investment gains and losses generated from the sale of debt securities, equity securities, investments in joint ventures and limited partnerships and from other than temporary impairments on investments other than debt securities. Also includes realized investment gains and losses are generated from prepayment premiums, recoveries of principal on previously impaired securities, provisions for losses on commercial mortgage and other loans, and fair value changes on embedded derivatives and derivatives that do not qualify for hedge accounting treatment, except those derivatives used in the Company's capacity as a broker or dealer.

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Other Than Temporary Impairment Losses

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This item represents the gross profit realized on the sale of debt or equity securities categorized neither as held-to-maturity nor trading securities.

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This item represents the gross loss realized on the sale of debt or equity securities categorized neither as held-to-maturity nor trading securities.

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Amount, before investment expense, of income earned from investments in securities and real estate. Includes, but is not limited to, real estate investment, policy loans, dividends, and interest. Excludes realized gain (loss) on investments.

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Amount of dividend income on nonoperating securities.

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Amount before accretion (amortization) of purchase discount (premium) of interest income on nonoperating securities.

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Amount of expenses related to the generation of investment income.

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Amount, after investment expense, of income earned from investments in securities and real estate. Includes, but is not limited to, real estate investment, policy loans, dividends, and interest. Excludes realized gain (loss) on investments.

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Amount after tax and reclassification adjustments of other comprehensive income (loss).

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Amount of tax expense (benefit) allocated to other comprehensive income (loss).

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Amount before tax and reclassification adjustments of unrealized holding gain (loss) on available-for-sale securities.

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The net realized gains or losses on investments during the period, not including gains or losses on securities separately or otherwise categorized as trading, available-for-sale, or held-to-maturity.

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