Investments - Additional Information (Detail) - USD ($)	Jun. 30, 2015	Dec. 31, 2014
Amortized Cost and Fair Value Debt Securities [Abstract]
Net unrealized gains on investments included in "AOCI"	$ 917,000,000	$ 1,200,000,000
Additional other than temporary impairment losses	0
Future capital call commitments	295,000,000
Commitments to purchase various privately placed debt securities, including bank loans	134,000,000
Commitments to sell various privately placed debt securities, including bank loans	$ 79,000,000