Derivative Financial Instruments - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Derivative Instruments And Hedging Activities Disclosure [Abstract]
Gains (losses) from changes in fair value of derivatives included in Investment gains (losses)	$ (5)	$ (1)	$ (3)	$ (2)
Gains (losses) from changes in fair value of derivatives held for trading included in Net investment income	(3)	5	(16)	1
Amount of gains recognized in OCI	19	15	1	49
Amount of gains (losses) reclassified from AOCI into income	6	18	19	27
Estimated amount of net unrealized gains associated with cash flow hedges that will be reclassified from AOCI into earnings during next twelve months	10		10
Net amounts recognized due to ineffectiveness	$ 1	$ 1	$ 1	$ 1