Schedule of Depreciation Expense (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Supplemental Financial Information [Line Items]
Depreciation expense	$ 353	$ 320	$ 698	$ 642