Change in Net Unrealized Gains (Losses) on Available-for-Sale Securities Reported in Accumulated Other Comprehensive Income (Loss) (Parenthetical) (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Components of Net Unrealized Investment Gains Losses Included in Accumulated Other Comprehensive Income Loss [Line Items]
Reclassification adjustments to net investment (gains) losses, taxes	$ 2	$ (6)	$ 4	$ (10)