Consolidated Statements of Comprehensive Income (unaudited) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Statement of Comprehensive Income [Abstract]
Net income	$ 1.3	$ 162.3
Derivative financial instruments:
Unrealized gains (losses) arising during the period, net of tax benefit (expense) of $(2.0) and $7.7	6.2	(25.6)
Reclassification adjustments for (gains) losses included in net income, net of tax benefit of $0.9 and $0.5	(0.9)	1.0
Defined benefit plans:
Amortization of prior service cost, net of tax benefit of $— and $0.1	0.0	0.2
Amortization of net actuarial losses, net of tax benefit of $— and $0.3	0.1	1.2
Other Comprehensive Income (Loss), Net of Tax, Total	5.4	(23.2)
Comprehensive income	6.7	139.1
Less: comprehensive income (loss) attributable to noncontrolling interest	(1.7)	0.9
Comprehensive income attributable to Trinity Industries, Inc.	$ 8.4	$ 138.2