Financial Statements for Guarantors of the Senior Notes - Statement of Cash Flows (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Condensed Cash Flow Statements, Captions [Line Items]
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	$ 350.8				$ 973.8				$ 350.8	$ 973.8	$ 741.6
Operating activities:
Net income	27.7	$ 28.3	$ 65.5	$ 41.6	540.0	$ 67.9	$ 54.0	$ 51.7	163.1	713.6	364.7
Income (Loss) from Discontinued Operations, Net of Tax, Attributable to Parent									(54.1)	(103.4)	(161.5)
Equity in earnings of subsidiaries, net of taxes									0.0	0.0	0.0
Other									165.2	(0.1)	634.3
Net cash provided by operating activities - continuing operations									274.2	610.1	837.5
Net cash provided by operating activities - discontinued									104.9	151.5	252.7
Net cash provided (required) by operating activities									379.1	761.6	1,090.2
Investing activities:
Decrease (increase) in short-term marketable securities									319.5	(84.8)	(149.8)
Proceeds from railcar lease fleet sales owned more than one year									230.5	360.7	37.7
Proceeds from disposition of property and other assets									17.1	7.8	11.0
Capital expenditures – leasing									(948.3)	(608.3)	(799.1)
Capital expenditures – manufacturing and other									(37.3)	(22.0)	(49.5)
Acquisitions, net of cash acquired									0.0
(Increase) decrease in investment in partially-owned subsidiaries									0.0	0.0	0.0
Divestitures									0.0
Other									6.2	0.3	6.8
Net cash required by investing activities - continuing operations									(412.3)	(346.3)	(942.9)
Net cash provided by investing activities - discontinued									(78.2)	(126.4)	(79.8)
Net cash provided (required) by investing activities									(490.5)	(472.7)	(1,022.7)
Financing activities:
Proceeds from issuance of common stock, net									0.0
Excess tax benefits from stock-based compensation									0.0	0.0	1.0
Payments to retire debt									(887.8)	(375.3)	(162.0)
Proceeds from issuance of debt									1,206.6	533.5	0.0
Shares repurchased									(506.1)	(79.4)	(34.7)
Dividends paid to common shareholders									(77.4)	(72.6)	(66.7)
Purchase of shares to satisfy employee tax on vested stock									(12.2)	(14.4)	(16.3)
Distributions to noncontrolling interest									(10.9)	(48.7)	(26.4)
Distributions to controlling interest in partially-owned leasing subsidiaries									0.0	0.0	0.0
Change in intercompany financing between entities									0.0	0.0	0.0
Other									(3.3)	0.2	(2.6)
Net cash provided (required) by financing activities - continuing									(291.1)	(56.7)	(307.7)
Cash distributions to Arcosa, Inc. in connection with the spin-off transaction									(220.5)	0.0	0.0
Net cash provided (required) by financing activities									(511.6)	(56.7)	(307.7)
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Period Increase (Decrease), Excluding Exchange Rate Effect									(623.0)	232.2	(240.2)
Cash and cash equivalents at beginning of period				778.6				741.6	778.6	741.6	981.8
Cash and cash equivalents at end of period	179.2				778.6				179.2	778.6	741.6
Reportable legal entities | Parent
Condensed Cash Flow Statements, Captions [Line Items]
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	154.7				763.9				154.7	763.9	537.9
Operating activities:
Net income									159.3	702.5	343.6
Income (Loss) from Discontinued Operations, Net of Tax, Attributable to Parent									16.0	(8.7)	(23.3)
Equity in earnings of subsidiaries, net of taxes									(300.0)	(617.1)	(353.7)
Other									(57.8)	115.6	85.4
Net cash provided by operating activities - continuing operations									(182.5)	192.3	52.0
Net cash provided by operating activities - discontinued									(16.0)	8.7	23.3
Net cash provided (required) by operating activities									(198.5)	201.0	75.3
Investing activities:
Decrease (increase) in short-term marketable securities									319.5	(84.8)	(149.8)
Proceeds from railcar lease fleet sales owned more than one year									0.0	0.0	0.0
Proceeds from disposition of property and other assets									0.2	0.0	0.0
Capital expenditures – leasing									0.0	0.0	0.0
Capital expenditures – manufacturing and other									(14.5)	(7.7)	(18.0)
Acquisitions, net of cash acquired									0.0
(Increase) decrease in investment in partially-owned subsidiaries									0.0	0.0	0.0
Divestitures									0.0
Other									0.0	0.0	0.0
Net cash required by investing activities - continuing operations									305.2	(92.5)	(167.8)
Net cash provided by investing activities - discontinued									0.0	0.0	0.0
Net cash provided (required) by investing activities									305.2	(92.5)	(167.8)
Financing activities:
Proceeds from issuance of common stock, net									0.0
Excess tax benefits from stock-based compensation									0.0		1.0
Payments to retire debt									(647.6)	0.0	0.0
Proceeds from issuance of debt									0.0	0.0
Shares repurchased									(506.1)	(79.4)	(34.7)
Dividends paid to common shareholders									(77.4)	(72.6)	(66.7)
Purchase of shares to satisfy employee tax on vested stock									(12.2)	(14.4)	(16.3)
Distributions to noncontrolling interest									0.0	0.0	0.0
Distributions to controlling interest in partially-owned leasing subsidiaries									0.0	0.0	0.0
Change in intercompany financing between entities									527.4	283.9	(21.2)
Other									0.0	0.0	0.0
Net cash provided (required) by financing activities - continuing									(715.9)
Cash distributions to Arcosa, Inc. in connection with the spin-off transaction									0.0
Net cash provided (required) by financing activities									(715.9)	117.5	(137.9)
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Period Increase (Decrease), Excluding Exchange Rate Effect									(609.2)	226.0	(230.4)
Cash and cash equivalents at beginning of period				763.9				537.9	763.9	537.9	768.3
Cash and cash equivalents at end of period	154.7				763.9				154.7	763.9	537.9
Reportable legal entities | Combined Guarantor Subsidiaries
Condensed Cash Flow Statements, Captions [Line Items]
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	4.1				1.6				4.1	1.6	5.3
Operating activities:
Net income									169.8	528.8	179.2
Income (Loss) from Discontinued Operations, Net of Tax, Attributable to Parent									0.0	0.0	0.0
Equity in earnings of subsidiaries, net of taxes									(107.5)	(59.3)	(45.8)
Other									115.2	(263.8)	436.5
Net cash provided by operating activities - continuing operations									177.5	205.7	569.9
Net cash provided by operating activities - discontinued									0.0	0.0	0.0
Net cash provided (required) by operating activities									177.5	205.7	569.9
Investing activities:
Decrease (increase) in short-term marketable securities									0.0	0.0	0.0
Proceeds from railcar lease fleet sales owned more than one year									759.5	663.3	27.3
Proceeds from disposition of property and other assets									4.1	1.4	0.3
Capital expenditures – leasing									(807.3)	(589.8)	(798.7)
Capital expenditures – manufacturing and other									(13.8)	(5.2)	(5.8)
Acquisitions, net of cash acquired									0.0
(Increase) decrease in investment in partially-owned subsidiaries									7.1	35.0	17.1
Divestitures									0.0
Other									(1.9)	0.0	1.5
Net cash required by investing activities - continuing operations									(52.3)	104.7	(758.3)
Net cash provided by investing activities - discontinued									0.0	0.0	0.0
Net cash provided (required) by investing activities									(52.3)	104.7	(758.3)
Financing activities:
Proceeds from issuance of common stock, net									0.0
Excess tax benefits from stock-based compensation									0.0		0.0
Payments to retire debt									(1.8)	(3.8)	(3.5)
Proceeds from issuance of debt									0.0	0.0
Shares repurchased									0.0	0.0	0.0
Dividends paid to common shareholders									0.0	0.0	0.0
Purchase of shares to satisfy employee tax on vested stock									0.0	0.0	0.0
Distributions to noncontrolling interest									0.0	0.0	0.0
Distributions to controlling interest in partially-owned leasing subsidiaries									0.0	0.0	0.0
Change in intercompany financing between entities									(120.9)	(310.3)	195.3
Other									0.0	0.0	0.0
Net cash provided (required) by financing activities - continuing									(122.7)
Cash distributions to Arcosa, Inc. in connection with the spin-off transaction									0.0
Net cash provided (required) by financing activities									(122.7)	(314.1)	191.8
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Period Increase (Decrease), Excluding Exchange Rate Effect									2.5	(3.7)	3.4
Cash and cash equivalents at beginning of period				1.6				5.3	1.6	5.3	1.9
Cash and cash equivalents at end of period	4.1				1.6				4.1	1.6	5.3
Reportable legal entities | Combined Non-Guarantor Subsidiaries
Condensed Cash Flow Statements, Captions [Line Items]
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	192.0				208.3				192.0	208.3	198.4
Operating activities:
Net income									192.6	110.4	159.4
Income (Loss) from Discontinued Operations, Net of Tax, Attributable to Parent									(70.1)	(94.7)	(138.2)
Equity in earnings of subsidiaries, net of taxes									0.0	0.0	0.0
Other									121.8	143.0	148.6
Net cash provided by operating activities - continuing operations									244.3	158.7	169.8
Net cash provided by operating activities - discontinued									120.9	142.8	229.4
Net cash provided (required) by operating activities									365.2	301.5	399.2
Investing activities:
Decrease (increase) in short-term marketable securities									0.0	0.0	0.0
Proceeds from railcar lease fleet sales owned more than one year									118.7	61.3	10.4
Proceeds from disposition of property and other assets									12.8	6.4	10.7
Capital expenditures – leasing									(788.7)	(382.4)	(0.4)
Capital expenditures – manufacturing and other									(9.0)	(9.1)	(25.7)
Acquisitions, net of cash acquired									0.0
(Increase) decrease in investment in partially-owned subsidiaries									0.0	0.0	0.0
Divestitures									0.0
Other									8.1	0.3	5.3
Net cash required by investing activities - continuing operations									(658.1)	(323.5)	0.3
Net cash provided by investing activities - discontinued									(78.2)	(126.4)	(79.8)
Net cash provided (required) by investing activities									(736.3)	(449.9)	(79.5)
Financing activities:
Proceeds from issuance of common stock, net									0.0
Excess tax benefits from stock-based compensation									0.0		0.0
Payments to retire debt									(238.4)	(371.5)	(158.5)
Proceeds from issuance of debt									1,206.6	533.5
Shares repurchased									0.0	0.0	0.0
Dividends paid to common shareholders									0.0	0.0	0.0
Purchase of shares to satisfy employee tax on vested stock									0.0	0.0	0.0
Distributions to noncontrolling interest									(10.9)	(48.7)	(26.4)
Distributions to controlling interest in partially-owned leasing subsidiaries									11.0	(35.0)	(17.1)
Change in intercompany financing between entities									(389.7)	79.8	(128.3)
Other									(3.3)	0.2	(2.6)
Net cash provided (required) by financing activities - continuing									575.3
Cash distributions to Arcosa, Inc. in connection with the spin-off transaction									(220.5)
Net cash provided (required) by financing activities									354.8	158.3	(332.9)
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Period Increase (Decrease), Excluding Exchange Rate Effect									(16.3)	9.9	(13.2)
Cash and cash equivalents at beginning of period				65.3				198.4	65.3	198.4	211.6
Cash and cash equivalents at end of period	59.1				65.3				59.1	65.3	198.4
Eliminations
Condensed Cash Flow Statements, Captions [Line Items]
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	0.0				0.0				0.0	0.0	0.0
Operating activities:
Net income									(358.6)	(628.1)	(317.5)
Income (Loss) from Discontinued Operations, Net of Tax, Attributable to Parent									0.0	0.0	0.0
Equity in earnings of subsidiaries, net of taxes									407.5	676.4	399.5
Other									(14.0)	5.1	(36.2)
Net cash provided by operating activities - continuing operations									34.9	53.4	45.8
Net cash provided by operating activities - discontinued									0.0	0.0	0.0
Net cash provided (required) by operating activities									34.9	53.4	45.8
Investing activities:
Decrease (increase) in short-term marketable securities									0.0	0.0	0.0
Proceeds from railcar lease fleet sales owned more than one year									(647.7)	(363.9)	0.0
Proceeds from disposition of property and other assets									0.0	0.0	0.0
Capital expenditures – leasing									647.7	363.9	0.0
Capital expenditures – manufacturing and other									0.0	0.0	0.0
Acquisitions, net of cash acquired									0.0
(Increase) decrease in investment in partially-owned subsidiaries									(7.1)	(35.0)	(17.1)
Divestitures									0.0
Other									0.0	0.0	0.0
Net cash required by investing activities - continuing operations									(7.1)	(35.0)	(17.1)
Net cash provided by investing activities - discontinued									0.0	0.0	0.0
Net cash provided (required) by investing activities									(7.1)	(35.0)	(17.1)
Financing activities:
Proceeds from issuance of common stock, net									0.0
Excess tax benefits from stock-based compensation									0.0		0.0
Payments to retire debt									0.0	0.0	0.0
Proceeds from issuance of debt									0.0	0.0
Shares repurchased									0.0	0.0	0.0
Dividends paid to common shareholders									0.0	0.0	0.0
Purchase of shares to satisfy employee tax on vested stock									0.0	0.0	0.0
Distributions to noncontrolling interest									0.0	0.0	0.0
Distributions to controlling interest in partially-owned leasing subsidiaries									(11.0)	35.0	17.1
Change in intercompany financing between entities									(16.8)	(53.4)	(45.8)
Other									0.0	0.0	0.0
Net cash provided (required) by financing activities - continuing									(27.8)
Cash distributions to Arcosa, Inc. in connection with the spin-off transaction									0.0
Net cash provided (required) by financing activities									(27.8)	(18.4)	(28.7)
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Period Increase (Decrease), Excluding Exchange Rate Effect									0.0	0.0	0.0
Cash and cash equivalents at beginning of period				$ (52.2)				$ 0.0	(52.2)	0.0	0.0
Cash and cash equivalents at end of period	$ (38.7)				$ (52.2)				$ (38.7)	$ (52.2)	$ 0.0