Fair Value of Financial Assets and Liabilities - Contractual Maturities of Investments (Detail) (Total fixed income securities, USD $) In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Total fixed income securities
Amortized Cost Basis
Due within one year	$ 1,946
Due after 1 year through 5 years	5,332
Due after 5 years through 10 years	548
Due after 10 years	289
Amortized Cost Basis	8,115	9,576
Aggregate Fair Value
Due within one year	1,946
Due after 1 year through 5 years	5,330
Due after 5 years through 10 years	540
Due after 10 years	287
Aggregate Fair Value	$ 8,103	$ 9,602