Fair Value of Financial Assets and Liabilities - Contractual Maturities of Investments (Detail) (Total fixed income securities, USD $) In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Total fixed income securities
Amortized Cost Basis
Due within one year	$ 2,695
Due after 1 year through 5 years	5,855
Due after 5 years through 10 years	519
Due after 10 years	507
Amortized Cost Basis	9,576	6,535
Aggregate Fair Value
Due within one year	2,697
Due after 1 year through 5 years	5,871
Due after 5 years through 10 years	531
Due after 10 years	503
Aggregate Fair Value	$ 9,602	$ 6,595