Debt and Credit Agreements - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Debt Instrument [Line Items]
Maturity period one	2013	2013
Maturity period two	2014	2014
Maturity period three	2019	2019
Outstanding amount under CP program	$ 0
Revolving Credit Agreement Proceeds	1,500
Consolidated Assets	Less than 115%
Secure indebtedness	15.00%
Interest Payments	112	136	174
Portfolio [Member]
Debt Instrument [Line Items]
Debt Instrument Collateralized obligations	46
Equipment [Member]
Debt Instrument [Line Items]
Debt Instrument Collateralized	62
Interest Rate Swap [Member]
Debt Instrument [Line Items]
Debt	$ 388	$ 388