Variable Interest Entities and Other Investments - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Variable Interest Entity [Line Items]
Expenses related to consolidated VIEs	$ 463	$ 408	$ 465
Revenue related to consolidated VIEs	3
LIHC investments [Member]
Variable Interest Entity [Line Items]
Carrying amount of assets, consolidated VIEs	287
Carrying amount of liabilities, consolidated VIEs	7
Number of LIHC investment fund	2
Trusts owned and lease railcars [Member]
Variable Interest Entity [Line Items]
Carrying amount of assets, consolidated VIEs	77
Consolidated VIEs, net of liabilities [Member]
Variable Interest Entity [Line Items]
Expenses related to consolidated VIEs	$ 31	$ 24