Investments - Additional Information (Detail) (USD $)	0 Months Ended
	Mar. 31, 2015	Mar. 31, 2015	Dec. 31, 2014
Amortized Cost and Fair Value Debt Securities [Abstract]
Net unrealized gains on investments included in "AOCI"		$ 1,200,000,000	$ 1,200,000,000
Additional other than temporary impairment losses	0
Future capital call commitments		338,000,000
Commitments to purchase various privately placed debt securities, including bank loans		82,000,000
Commitments to sell various privately placed debt securities, including bank loans		$ 71,000,000