Interest Income and Interest Expense (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Disclosure Interest Income And Interest Expense [Abstract]
Interest expense on senior notes	$ 187	$ 152	$ 546	$ 494
Interest expense on credit facilities	13	18	51	49
Interest expense on term loans	112	0	173	0
(Gains) losses on interest rate derivatives	(2)	0	(4)	19
Amortization of loan discount and other	24	8	67	30
Capitalized interest	(298)	(174)	(770)	(555)
Total interest expense	$ 36	$ 4	$ 63	$ 37