Receivables - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		12 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2012
Deferred purchase price receivable		$ 254
Additional funding received	45		205
Purchase price receivable	15
Accounts receivables	4,390
Cash collections	4,125
Minimum [Member]
Funding of customer receivables sold	50
Maximum [Member]
Funding of customer receivables sold	$ 250