Investments - Schedule of Net Change in Unrealized Gains (Losses) on Available-for-Sale Investments (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Schedule of Available-for-sale Securities [Line Items]
Total net change in unrealized gains on available-for-sale investments	$ 1,517	$ (2,556)	$ 1,875
Fixed Maturity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Total net change in unrealized gains on available-for-sale investments	1,511	(2,541)	1,871
Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Total net change in unrealized gains on available-for-sale investments	6	(15)	5
Other [Member]
Schedule of Available-for-sale Securities [Line Items]
Total net change in unrealized gains on available-for-sale investments			$ (1)