Fair Values of Financial Instruments - Carrying Values and Fair Values of Financial Instruments (Detail) - USD ($) $ in Millions	Sep. 30, 2015	Dec. 31, 2014
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short Term Investments	$ 3,052	$ 1,318
Fixed maturities	37,016	38,780
Equity securities	1,771	1,964
Long Term Debt	3,300	3,300
Carrying Value [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short Term Investments	3,052	1,318
Fixed maturities	37,016	38,780
Equity securities	1,771	1,964
Long Term Debt	3,300	3,300
Fair Value [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short Term Investments	3,052	1,318
Fixed maturities	37,016	38,780
Equity securities	1,771	1,964
Long Term Debt	$ 3,788	$ 4,013

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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Carrying amount of long-term debt, net of unamortized discount or premium, including current and noncurrent amounts. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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Investments which are intended to be sold in the short term (usually less than one year or the normal operating cycle, whichever is longer) including trading securities, available-for-sale securities, held-to-maturity securities, and other short-term investments not otherwise listed in the existing taxonomy.

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