Interest Cost Components - Schedule of Interest Cost Components (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Amount charged to expense	$ 490	$ 524	$ 494
Amount capitalized	93	101	96
Interest costs, total	$ 583	$ 625	$ 590