Investments - Additional Information (Detail) - USD ($)	Jun. 30, 2016	Dec. 31, 2015
Investments, Debt and Equity Securities [Abstract]
Net unrealized gains on investments included in "AOCI"	$ 1,500,000,000	$ 996,000,000
Additional other than temporary impairment losses	0
Amortized cost of marketable securities unrealized loss position	$ 0