Financial Statements for Guarantors of the Senior Notes - Statement of Cash Flows (Details) - USD ($) $ in Millions	3 Months Ended				6 Months Ended
	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2019	Jun. 30, 2018
Operating activities:
Net income	$ 36.8	$ 30.1	$ 65.5	$ 41.6	$ 66.9	$ 107.1
Income (Loss) from Discontinued Operations, Net of Tax, Attributable to Parent					1.9	(54.6)
Equity in earnings of subsidiaries, net of taxes	0.0		0.0		0.0	0.0
Other					(65.9)	167.3
Net Cash Provided by (Used in) Operating Activities, Continuing Operations					2.9	219.8
Cash Provided by (Used in) Operating Activities, Discontinued Operations					0.0	128.5
Net Cash Provided by (Used in) Operating Activities					2.9	348.3
Investing activities:
(Increase) decrease in short-term marketable securities					0.0	294.5
Proceeds from railcar lease fleet sales owned more than one year					99.9	56.4
Proceeds from dispositions of property and other assets					14.3	4.4
Capital expenditures – leasing					(690.9)	(503.2)
Capital expenditures – manufacturing and other					(34.0)	(13.5)
(Increase) decrease in investment in partially-owned subsidiaries					0.0	0.0
Other					(1.2)	1.3
Net Cash Provided by (Used in) Investing Activities, Continuing Operations					(611.9)	(160.1)
Cash Provided by (Used in) Investing Activities, Discontinued Operations					0.0	(44.3)
Net cash (used in) provided by investing activities					(611.9)	(204.4)
Financing activities:
Payments to retire debt					(1,044.9)	(674.5)
Proceeds from issuance of debt					1,626.9	478.0
Shares repurchased					(59.0)	(102.2)
Dividends paid to common shareholders					(39.5)	(39.3)
Purchase of shares to satisfy employee tax on vested stock					(7.9)	(11.3)
Distributions to noncontrolling interest					(0.9)	(10.3)
Distributions to controlling interest in partially-owned subsidiaries					0.0	0.0
Change in intercompany financing between entities					0.0	0.0
Other					0.0	(3.2)
Net cash provided (used in) by financing activities					474.7	(362.8)
Net (decrease) increase in cash, cash equivalents, and restricted cash					(134.3)	(218.9)
Cash, cash equivalents, and restricted cash at beginning of period		350.8		973.8	350.8	973.8
Cash, cash equivalents, and restricted cash at end of period	216.5		754.9		216.5	754.9
Reportable legal entities | Parent
Operating activities:
Net income	36.4		64.1		67.0	104.3
Income (Loss) from Discontinued Operations, Net of Tax, Attributable to Parent					1.6	4.5
Equity in earnings of subsidiaries, net of taxes	(65.6)		(102.6)		(119.8)	(183.9)
Other					(16.1)	(35.1)
Net Cash Provided by (Used in) Operating Activities, Continuing Operations						(110.2)
Cash Provided by (Used in) Operating Activities, Discontinued Operations						(4.5)
Net Cash Provided by (Used in) Operating Activities					(67.3)	(114.7)
Investing activities:
(Increase) decrease in short-term marketable securities						294.5
Proceeds from railcar lease fleet sales owned more than one year					0.0	0.0
Proceeds from dispositions of property and other assets					0.0	0.1
Capital expenditures – leasing					0.0	0.0
Capital expenditures – manufacturing and other					(2.8)	(2.6)
(Increase) decrease in investment in partially-owned subsidiaries					0.0	0.0
Other					0.0	0.0
Net Cash Provided by (Used in) Investing Activities, Continuing Operations						292.0
Cash Provided by (Used in) Investing Activities, Discontinued Operations						0.0
Net cash (used in) provided by investing activities					(2.8)	292.0
Financing activities:
Payments to retire debt					(550.0)	(619.7)
Proceeds from issuance of debt					550.0	0.0
Shares repurchased					(59.0)	(102.2)
Dividends paid to common shareholders					(39.5)	(39.3)
Purchase of shares to satisfy employee tax on vested stock					(7.9)	(11.3)
Distributions to noncontrolling interest					0.0	0.0
Distributions to controlling interest in partially-owned subsidiaries					0.0	0.0
Change in intercompany financing between entities					115.1	422.2
Other						0.0
Net cash provided (used in) by financing activities					8.7	(350.3)
Net (decrease) increase in cash, cash equivalents, and restricted cash					(61.4)	(173.0)
Cash, cash equivalents, and restricted cash at beginning of period		154.7		763.9	154.7	763.9
Cash, cash equivalents, and restricted cash at end of period	93.3		590.9		93.3	590.9
Reportable legal entities | Combined Guarantor Subsidiaries
Operating activities:
Net income	50.9		56.1		93.6	96.5
Income (Loss) from Discontinued Operations, Net of Tax, Attributable to Parent					0.0	0.0
Equity in earnings of subsidiaries, net of taxes	(10.6)		(13.4)		(26.0)	(27.2)
Other					(169.6)	122.6
Net Cash Provided by (Used in) Operating Activities, Continuing Operations						191.9
Cash Provided by (Used in) Operating Activities, Discontinued Operations						0.0
Net Cash Provided by (Used in) Operating Activities					(102.0)	191.9
Investing activities:
(Increase) decrease in short-term marketable securities						0.0
Proceeds from railcar lease fleet sales owned more than one year					999.2	700.1
Proceeds from dispositions of property and other assets					6.0	1.9
Capital expenditures – leasing					(735.5)	(462.3)
Capital expenditures – manufacturing and other					(19.9)	(4.1)
(Increase) decrease in investment in partially-owned subsidiaries					0.7	4.9
Other					0.0	0.0
Net Cash Provided by (Used in) Investing Activities, Continuing Operations						240.5
Cash Provided by (Used in) Investing Activities, Discontinued Operations						0.0
Net cash (used in) provided by investing activities					250.5	240.5
Financing activities:
Payments to retire debt					0.0	(1.5)
Proceeds from issuance of debt					0.0	0.0
Shares repurchased					0.0	0.0
Dividends paid to common shareholders					0.0	0.0
Purchase of shares to satisfy employee tax on vested stock					0.0	0.0
Distributions to noncontrolling interest					0.0	0.0
Distributions to controlling interest in partially-owned subsidiaries					0.0	0.0
Change in intercompany financing between entities					(152.6)	(429.8)
Other						0.0
Net cash provided (used in) by financing activities					(152.6)	(431.3)
Net (decrease) increase in cash, cash equivalents, and restricted cash					(4.1)	1.1
Cash, cash equivalents, and restricted cash at beginning of period		4.1		1.6	4.1	1.6
Cash, cash equivalents, and restricted cash at end of period	0.0		2.7		0.0	2.7
Reportable legal entities | Combined Non-Guarantor Subsidiaries
Operating activities:
Net income	15.4		56.9		36.1	107.4
Income (Loss) from Discontinued Operations, Net of Tax, Attributable to Parent					0.3	(59.1)
Equity in earnings of subsidiaries, net of taxes	(6.6)		(7.6)		(11.6)	(12.9)
Other					142.1	100.1
Net Cash Provided by (Used in) Operating Activities, Continuing Operations						135.5
Cash Provided by (Used in) Operating Activities, Discontinued Operations						133.0
Net Cash Provided by (Used in) Operating Activities					166.9	268.5
Investing activities:
(Increase) decrease in short-term marketable securities						0.0
Proceeds from railcar lease fleet sales owned more than one year					139.3	4.0
Proceeds from dispositions of property and other assets					8.3	2.4
Capital expenditures – leasing					(994.0)	(688.6)
Capital expenditures – manufacturing and other					(11.3)	(6.8)
(Increase) decrease in investment in partially-owned subsidiaries					0.0	0.0
Other					(1.2)	1.3
Net Cash Provided by (Used in) Investing Activities, Continuing Operations						(687.7)
Cash Provided by (Used in) Investing Activities, Discontinued Operations						(44.3)
Net cash (used in) provided by investing activities					(858.9)	(732.0)
Financing activities:
Payments to retire debt					(494.9)	(53.3)
Proceeds from issuance of debt					1,076.9	478.0
Shares repurchased					0.0	0.0
Dividends paid to common shareholders					0.0	0.0
Purchase of shares to satisfy employee tax on vested stock					0.0	0.0
Distributions to noncontrolling interest					(0.9)	(10.3)
Distributions to controlling interest in partially-owned subsidiaries					(0.7)	(4.9)
Change in intercompany financing between entities					42.8	10.2
Other						(3.2)
Net cash provided (used in) by financing activities					623.2	416.5
Net (decrease) increase in cash, cash equivalents, and restricted cash					(68.8)	(47.0)
Cash, cash equivalents, and restricted cash at beginning of period		192.0		208.3	192.0	208.3
Cash, cash equivalents, and restricted cash at end of period	123.2		161.3		123.2	161.3
Eliminations
Operating activities:
Net income	(65.9)		(111.6)		(129.8)	(201.1)
Income (Loss) from Discontinued Operations, Net of Tax, Attributable to Parent					0.0	0.0
Equity in earnings of subsidiaries, net of taxes	82.8		123.6		157.4	224.0
Other					(22.3)	(20.3)
Net Cash Provided by (Used in) Operating Activities, Continuing Operations						2.6
Cash Provided by (Used in) Operating Activities, Discontinued Operations						0.0
Net Cash Provided by (Used in) Operating Activities					5.3	2.6
Investing activities:
(Increase) decrease in short-term marketable securities						0.0
Proceeds from railcar lease fleet sales owned more than one year					(1,038.6)	(647.7)
Proceeds from dispositions of property and other assets					0.0	0.0
Capital expenditures – leasing					1,038.6	647.7
Capital expenditures – manufacturing and other					0.0	0.0
(Increase) decrease in investment in partially-owned subsidiaries					(0.7)	(4.9)
Other					0.0	0.0
Net Cash Provided by (Used in) Investing Activities, Continuing Operations						(4.9)
Cash Provided by (Used in) Investing Activities, Discontinued Operations						0.0
Net cash (used in) provided by investing activities					(0.7)	(4.9)
Financing activities:
Payments to retire debt					0.0	0.0
Proceeds from issuance of debt					0.0	0.0
Shares repurchased					0.0	0.0
Dividends paid to common shareholders					0.0	0.0
Purchase of shares to satisfy employee tax on vested stock					0.0	0.0
Distributions to noncontrolling interest					0.0	0.0
Distributions to controlling interest in partially-owned subsidiaries					0.7	4.9
Change in intercompany financing between entities					(5.3)	(2.6)
Other						0.0
Net cash provided (used in) by financing activities					(4.6)	2.3
Net (decrease) increase in cash, cash equivalents, and restricted cash					0.0	0.0
Cash, cash equivalents, and restricted cash at beginning of period		$ 0.0		$ 0.0	0.0	0.0
Cash, cash equivalents, and restricted cash at end of period	$ 0.0		$ 0.0		$ 0.0	$ 0.0