Debt - Narrative (Details)		6 Months Ended
	Apr. 11, 2018	Jun. 30, 2018 USD ($)		Jun. 02, 2018 USD ($)	Jun. 01, 2018 USD ($)	May 30, 2018 USD ($)	Apr. 23, 2018 USD ($)	Dec. 31, 2017 USD ($)
Debt Instrument [Line Items]
Conversion ratio of convertible debt	41.4390
Non-recourse debt		$ 2,835,100,000						$ 2,401,200,000
Non-recourse debt		2,802,900,000						2,375,600,000
Redemption of convertible subordinated notes		152,900,000
Convertible subordinated notes
Debt Instrument [Line Items]
Debt Conversion, Converted Instrument, Settled in Par		800,000
Debt Conversion, Converted Instrument, Amount		646,600,000
Convertible debt face amount							$ 1,000
Convertible Debt				$ 449,300,000		$ 448,500,000
Corporate | Convertible subordinated notes | 3 7/8% Convertible Subordinated Notes Due 2036
Debt Instrument [Line Items]
Capital in excess of par value related to the Convertible Subordinated Notes' conversion options		$ 92,500,000
Effective annual interest rate yield		8.42%
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
Railcar Leasing and Management Services Group
Debt Instrument [Line Items]
Non-recourse debt		2,802,900,000						2,375,600,000
Wholly-owned subsidiaries
Debt Instrument [Line Items]
Non-recourse debt		1,473,000,000	[1]					1,024,800,000
Wholly-owned subsidiaries | Railcar Leasing and Management Services Group
Debt Instrument [Line Items]
Non-recourse debt		1,491,300,000						1,035,900,000
Non-recourse debt		1,473,000,000						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		286,000,000						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		598,900,000
Non-recourse debt		151,100,000						150,700,000
TILC | 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		3.74%
TILC warehouse loan, amount outstanding		$ 151,100,000
Partially-owned subsidiaries
Debt Instrument [Line Items]
Non-recourse debt		1,329,900,000	[1]					1,350,800,000
Partially-owned subsidiaries | Railcar Leasing and Management Services Group
Debt Instrument [Line Items]
Non-recourse debt		1,343,500,000						1,365,300,000
Non-recourse debt		1,329,900,000						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		951,200,000						$ 962,500,000
Trinity Rail Leasing 2018 | Secured debt | 2018 secured railcar equipment notes
Debt Instrument [Line Items]
Debt instrument, issued amount					$ 482,500,000
Trinity Rail Leasing 2018 | Secured debt | 2018 Secured Railcar Equipment Class A-1 Note
Debt Instrument [Line Items]
Debt instrument, issued amount					$ 200,000,000
Debt instrument, stated interest rate					3.82%
Trinity Rail Leasing 2018 | Secured debt | 2018 Secured Railcar Equipment Class A-2 Note
Debt Instrument [Line Items]
Debt instrument, issued amount					$ 282,500,000
Debt instrument, stated interest rate					4.62%
Additional Paid-in Capital [Member]
Debt Instrument [Line Items]
Redemption of convertible subordinated notes		$ 152,900,000

[1] (unaudited)