Fair Values of Financial Instruments - Carrying Values and Fair Values of Financial Instruments (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short term investments	$ 1,881	$ 2,528
Fixed maturities	37,610	38,076
Equity securities	1,821	1,663
Other invested assets	1,665	1,954
Long Term Debt	3,300	3,575
Carrying Value [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short term investments	1,881	2,528
Fixed maturities	37,610	38,076
Equity securities	1,821	1,663
Other invested assets		46
Long Term Debt	3,300	3,575
Fair Value [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short term investments	1,881	2,528
Fixed maturities	37,610	38,076
Equity securities	1,821	1,663
Other invested assets		46
Long Term Debt	$ 3,834	$ 4,372