Railcar Leasing and Management Services Group - Schedule of proceeds from leased railcars (Details) - USD ($) $ in Millions	3 Months Ended			9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019		Sep. 30, 2020	Sep. 30, 2019
Property Subject to or Available for Operating Lease [Line Items]
Sales-type lease revenues	$ 0.0	$ 26.3		$ 0.0	$ 60.5
Operating profit on sales of leased railcars:	72.9	120.3		(161.4)	319.1
Operating Segments [Member] | Railcar Leasing and Management Services Group [Member]
Property Subject to or Available for Operating Lease [Line Items]
Operating profit on sales of leased railcars:	$ 89.7	$ 115.7		$ 265.5	$ 306.3
Operating profit margin on sales of leased railcars:	48.80%	35.40%		43.30%	38.10%
Operating Segments [Member] | Railcar Owned One Year or Less [Member] | Railcar Leasing and Management Services Group [Member]
Property Subject to or Available for Operating Lease [Line Items]
Sales of leased railcars:	$ 0.0	$ 136.3	[1]	$ 54.4	$ 237.3	[1]
Operating profit on sales of leased railcars:	$ 0.0	$ 17.8		$ 0.4	$ 27.0
Operating profit margin on sales of leased railcars:	0.00%	13.10%		0.70%	11.40%
Operating Segments [Member] | Railcar Owned Greater than One Year [Member] | Railcar Leasing and Management Services Group [Member]
Property Subject to or Available for Operating Lease [Line Items]
Sales of leased railcars:	$ 6.5	$ 75.1		$ 138.7	$ 175.0
Operating profit on sales of leased railcars:	$ 2.9	$ 18.1		$ 17.3	$ 44.7
Operating profit margin on sales of leased railcars:	44.60%	24.10%		12.50%	25.50%
Operating Segments [Member] | Sales of Leased Railcars [Domain] | Railcar Leasing and Management Services Group [Member]
Property Subject to or Available for Operating Lease [Line Items]
Sales of leased railcars:	$ 6.5	$ 211.4		$ 193.1	$ 412.3
Operating profit on sales of leased railcars:	$ 2.9	$ 35.9		$ 17.7	$ 71.7
Operating profit margin on sales of leased railcars:	44.60%	17.00%		9.20%	17.40%

[1] Includes revenues associated with sales-type leases of $26.3 million and $60.5 million for the three and nine months ended September 30, 2019, respectively.