Accumulated Other Comprehensive Income Balances (Detail) (USD $) In Millions, unless otherwise specified	6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011
Beginning Balance	$ 8	$ 16
Other net changes	146	29
Ending Balance	154	45
Net unrealized gain on securities available for sale
Beginning Balance	10	17
Other net changes	145	28
Ending Balance	155	45
Other
Beginning Balance	(2)	(1)
Other net changes	1	1
Ending Balance	$ (1)