Allowance for Losses on Receivables (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
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for losses on receivables at beginning of period			$ 53	$ 87
Recovery of losses	(1)	(11)	(5)	(20)
Write-offs				(11)
Allowance for losses on receivables at end of period	48	56	48	56
Allowance as a percentage of total receivables	2.20%	2.40%	2.20%	2.40%
Allowance for losses on receivables collectively evaluated for impairment	$ 48	$ 56	$ 48	$ 56