Investments - Additional Information (Detail) (USD $)	0 Months Ended
	Sep. 30, 2014	Sep. 30, 2014	Dec. 31, 2013
Investments, Debt and Equity Securities [Abstract]
Net unrealized gains on investments included in AOCI		$ 873,000,000	$ 478,000,000
Additional other than temporary impairment losses	0
Future capital call commitments		365,000,000
Commitments to purchase various privately placed debt securities, including bank loans		140,000,000
Commitments to sell various privately placed debt securities, including bank loans		$ 103,000,000