Fair Value of Financial Assets and Liabilities - Contractual Maturities of Investments (Detail) - Fixed income securities - USD ($) $ in Millions	Jun. 30, 2015	Dec. 31, 2014
Amortized Cost Basis
Due within one year	$ 1,932
Due after 1 year through 5 years	5,885
Due after 5 years through 10 years	559
Due after 10 years	338
Amortized Cost	8,714	$ 8,115
Aggregate Fair Value
Due within one year	1,932
Due after 1 year through 5 years	5,886
Due after 5 years through 10 years	552
Due after 10 years	336
Aggregate Fair Value	$ 8,706	$ 8,103