Investments in fixed maturity securities - Amortized cost and estimated fair value of securities with fixed maturities (Detail) (Fixed Maturities [Member], USD $) In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Summary of Investment Holdings [Line Items]
Due in one year or less - fair value	$ 8,499
Due after one year through five years - fair value	11,499
Due after five years through ten years - fair value	4,021
Due after ten years - fair value	3,311
Fair Value of Investments	29,370	38,425
Due in one year or less - amortized cost	8,371
Due after one year through five years - amortized cost	11,022
Due after five years through ten years - amortized cost	3,601
Due after ten years - amortized cost	2,940
Total - amortized cost	27,764	34,520
Mortgage-backed securities [Member]
Summary of Investment Holdings [Line Items]
Mortgage-backed securities - fair value	2,040
Mortgage-backed securities - amortized cost	$ 1,830