Debt - The Carrying Value of Debt (Parenthetical) (Detail)	9 Months Ended
	Sep. 30, 2012
Debt Instrument [Line Items]
Floating rate note due in 2023	1.62%
Capital lease obligation	1.03%
Maximum [Member]
Debt Instrument [Line Items]
Fixed rate notes due through 2019	7.58%
Non-recourse debt	4.84%
Minimum [Member]
Debt Instrument [Line Items]
Fixed rate notes due through 2019	2.13%
Non-recourse debt	1.33%