Fair Value Accounting - Carrying amounts and estimated fair values of long-term debt (Details) - USD ($) $ in Millions	Sep. 30, 2017		Dec. 31, 2016
Carrying amounts and estimated fair values of long-term debt
Convertible subordinated notes	$ 879.3		$ 881.5
Less: unamortized discount	(13.2)	[1]	(27.1)
Less: unamortized debt issuance costs	(3.2)		(3.8)
Recourse, net of unamortized discount and unamortized debt issuance costs	862.9	[1]	850.6
Non-recourse debt	2,440.5		2,232.4
Less: unamortized debt issuance costs	(27.0)		(26.4)
Non-recourse debt, net of unamortized debt issuance costs	2,413.5		2,206.0
Total debt	3,276.4	[1]	3,056.6
Carrying Value
Carrying amounts and estimated fair values of long-term debt
Long-term debt, including unamortized debt issuance costs, net of unamortized discount	866.1		854.4
Less: unamortized debt issuance costs	(3.2)		(3.8)
Recourse, net of unamortized discount and unamortized debt issuance costs	862.9		850.6
Non-recourse debt	2,440.5		2,232.4
Less: unamortized debt issuance costs	(27.0)		(26.4)
Non-recourse debt, net of unamortized debt issuance costs	2,413.5		2,206.0
Total debt	3,276.4		3,056.6
Carrying Value | 2006 secured railcar equipment notes
Carrying amounts and estimated fair values of long-term debt
Non-recourse debt	164.4		194.2
Carrying Value | 2009 secured railcar equipment notes
Carrying amounts and estimated fair values of long-term debt
Non-recourse debt	167.7		172.5
Carrying Value | 2010 secured railcar equipment notes
Carrying amounts and estimated fair values of long-term debt
Non-recourse debt	269.9		280.6
Carrying Value | 2017 promissory notes
Carrying amounts and estimated fair values of long-term debt
Non-recourse debt	297.4		0.0
Carrying Value | TRL 2012 secured railcar equipment notes
Carrying amounts and estimated fair values of long-term debt
Non-recourse debt	408.2		425.5
Carrying Value | TRIP Master Funding secured railcar equipment notes
Carrying amounts and estimated fair values of long-term debt
Non-recourse debt	966.2		955.5
Carrying Value | Senior notes
Carrying amounts and estimated fair values of long-term debt
Long-term debt, including unamortized debt issuance costs, net of unamortized discount	399.7		399.6
Carrying Value | Convertible subordinated notes
Carrying amounts and estimated fair values of long-term debt
Long-term debt, including unamortized debt issuance costs, net of unamortized discount	436.5		422.7
Convertible subordinated notes	449.4		449.4
Less: unamortized discount	(12.9)		(26.7)
Carrying Value | Capital lease obligations
Carrying amounts and estimated fair values of long-term debt
Long-term debt, including unamortized debt issuance costs, net of unamortized discount	29.4		32.1
Carrying Value | Other
Carrying amounts and estimated fair values of long-term debt
Long-term debt, including unamortized debt issuance costs, net of unamortized discount	0.5		0.0
Carrying Value | Line of credit | TILC warehouse facility | Revolving credit facility
Carrying amounts and estimated fair values of long-term debt
Non-recourse debt	166.7		204.1
Estimated Fair Value
Carrying amounts and estimated fair values of long-term debt
Long-term debt, including unamortized debt issuance costs, net of unamortized discount	1,044.0		993.9
Non-recourse debt	2,514.5		2,236.0
Total debt	3,558.5		3,229.9
Estimated Fair Value | 2006 secured railcar equipment notes
Carrying amounts and estimated fair values of long-term debt
Non-recourse debt	177.6		201.5
Estimated Fair Value | 2009 secured railcar equipment notes
Carrying amounts and estimated fair values of long-term debt
Non-recourse debt	179.2		189.9
Estimated Fair Value | 2010 secured railcar equipment notes
Carrying amounts and estimated fair values of long-term debt
Non-recourse debt	284.4		284.3
Estimated Fair Value | 2017 promissory notes
Carrying amounts and estimated fair values of long-term debt
Non-recourse debt	297.4		0.0
Estimated Fair Value | TRL 2012 secured railcar equipment notes
Carrying amounts and estimated fair values of long-term debt
Non-recourse debt	398.1		395.6
Estimated Fair Value | TRIP Master Funding secured railcar equipment notes
Carrying amounts and estimated fair values of long-term debt
Non-recourse debt	1,011.1		960.6
Estimated Fair Value | Senior notes
Carrying amounts and estimated fair values of long-term debt
Long-term debt, including unamortized debt issuance costs, net of unamortized discount	409.0		386.3
Estimated Fair Value | Convertible subordinated notes
Carrying amounts and estimated fair values of long-term debt
Convertible subordinated notes	605.1		575.5
Estimated Fair Value | Capital lease obligations
Carrying amounts and estimated fair values of long-term debt
Long-term debt, including unamortized debt issuance costs, net of unamortized discount	29.4		32.1
Estimated Fair Value | Other
Carrying amounts and estimated fair values of long-term debt
Long-term debt, including unamortized debt issuance costs, net of unamortized discount	0.5		0.0
Estimated Fair Value | Line of credit | TILC warehouse facility | Revolving credit facility
Carrying amounts and estimated fair values of long-term debt
Non-recourse debt	$ 166.7		$ 204.1

[1] (unaudited)