Income Taxes - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Dec. 31, 2011
Income Taxes [Line Items]
Income Tax refundable	$ 567		$ 0
Increase in income tax refundable	567	0
Net deferred tax assets	396
Increase in net deferred tax assets	$ 336