Fair Values of Financial Instruments - Carrying Values and Fair Values of Financial Instruments (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short term investments	$ 2,284	$ 1,893
Fixed maturities	38,217	37,184
Equity securities	1,613	1,512
Long Term Debt	3,575	3,575
Carrying Value [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short term investments	2,284	1,893
Fixed maturities	38,217	37,184
Equity securities	1,613	1,512
Long Term Debt	3,575	3,575
Fair Value [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short term investments	2,284	1,893
Fixed maturities	38,217	37,184
Equity securities	1,613	1,512
Long Term Debt	$ 4,427	$ 4,085

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

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+ Details

- Definition

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

+ References

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+ Details

- Definition

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.

+ References+ Details

- Definition

Other investments not otherwise specified in the taxonomy that will be realized in a short period of time, usually less than one year or the normal operating cycle, whichever is longer.

+ References+ Details