Debt - Narrative (Details)		3 Months Ended		12 Months Ended
	Apr. 11, 2018	Mar. 31, 2018 USD ($) day $ / shares		Dec. 31, 2017 USD ($)	Apr. 23, 2018 USD ($)
Debt Instrument [Line Items]
Convertible subordinated notes		$ 877,300,000		$ 878,200,000
Non-recourse debt		2,380,300,000		2,401,200,000
Non-recourse debt		$ 2,352,400,000		2,375,600,000
Corporate | Convertible subordinated notes | 3 7/8% Convertible Subordinated Notes Due 2036 [Member]
Debt Instrument [Line Items]
Debt Instrument, Redemption Price, Percentage		100.00%
Capital in excess of par value related to the Convertible Subordinated Notes' conversion options		$ 92,500,000		92,500,000
Effective annual interest rate yield		8.42%
Percentage of conversion price at which Convertible Subordinated Notes are convertible (greater than or equal to)		130.00%
Convertible debt, trading days threshold | day		20
Convertible debt, consecutive trading days threshold | day		30
Conversion price of convertible subordinated notes (in dollars per share) | $ / shares		$ 24.21
Corporate | Revolving credit facility | Line of credit
Debt Instrument [Line Items]
Revolving credit facility		$ 600,000,000
Remaining borrowing capacity on revolving credit facility		521,200,000
Borrowing under revolving credit facility exclusive of letters of credit		0
Corporate | Letter of credit | Line of credit
Debt Instrument [Line Items]
Used revolving credit facility for letters of credit		78,800,000
Letters of credit expiring in next fiscal year		78,000,000
Railcar Leasing and Management Services Group
Debt Instrument [Line Items]
Non-recourse debt		2,352,400,000		2,375,600,000
Wholly-owned subsidiaries
Debt Instrument [Line Items]
Non-recourse debt		1,012,300,000	[1]	1,024,800,000
Wholly-owned subsidiaries | Railcar Leasing and Management Services Group
Debt Instrument [Line Items]
Non-recourse debt		1,026,200,000		1,035,900,000
Non-recourse debt		1,012,300,000		1,024,800,000
Wholly-owned subsidiaries | Railcar Leasing and Management Services Group | Promissory note | 2017 promissory notes
Debt Instrument [Line Items]
Non-recourse debt		289,800,000		293,600,000
Wholly-owned subsidiaries | Railcar Leasing and Management Services Group | Revolving credit facility | Line of credit | TILC warehouse facility
Debt Instrument [Line Items]
TILC warehouse loan, unused portion		595,500,000
Non-recourse debt		154,500,000		150,700,000
TILC [Member] | Railcar Leasing and Management Services Group | Revolving credit facility | Line of credit | TILC warehouse facility
Debt Instrument [Line Items]
Revolving credit facility		$ 750,000,000		1,000,000,000
Effective annual interest rate yield		3.57%
TILC warehouse loan, amount outstanding		$ 154,500,000
Partially-owned subsidiaries
Debt Instrument [Line Items]
Non-recourse debt		1,340,100,000	[1]	1,350,800,000
Partially-owned subsidiaries | Railcar Leasing and Management Services Group
Debt Instrument [Line Items]
Non-recourse debt		1,354,100,000		1,365,300,000
Non-recourse debt		1,340,100,000		1,350,800,000
Partially-owned subsidiaries | Railcar Leasing and Management Services Group | Secured debt | TRIP Master Funding secured railcar equipment notes
Debt Instrument [Line Items]
Non-recourse debt		$ 957,000,000		$ 962,500,000
Subsequent Event
Debt Instrument [Line Items]
Conversion ratio of convertible debt	41.439
Subsequent Event | Convertible subordinated notes
Debt Instrument [Line Items]
Convertible subordinated notes					$ 449,400,000
Convertible debt face amount					$ 1,000.0

[1] (unaudited)