Investments in fixed maturity securities - Amortized cost and estimated fair value of securities with fixed maturities (Detail) (USD $) In Millions	Jun. 30, 2011	Dec. 31, 2010
Amortized cost and estimated fair value of securities with fixed maturities [Line Items]
Due in one year or less - fair value	$ 8,515
Due after one year through five years - fair value	15,801
Due after five years through ten years - fair value	5,428
Due after ten years - fair value	3,232
Mortgage-backed securities - fair value	2,878
Fair Value	35,854	34,883
Due in one year or less - amortized cost	8,314
Due after one year through five years - amortized cost	14,485
Due after five years through ten years - amortized cost	4,578
Due after ten years - amortized cost	2,663
Mortgage-backed securities - amortized cost	2,573
Total - amortized cost	$ 32,613	$ 31,839