Quarterly Results - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended			12 Months Ended
	Dec. 31, 2012	Sep. 30, 2011	Mar. 31, 2011	Dec. 31, 2011	Dec. 31, 2010
Quarterly Financial Information [Line Items]
Income tax expense (benefit)	$ 54
Gain (loss) on extinguishment of debt			(53)	(53)	(7)
Gain on sale of equity investments		$ 60		$ 60