Accumulated Other Comprehensive Loss - Changes in accumulated other comprehensive loss (Details) - USD ($) $ in Millions	3 Months Ended				6 Months Ended
	Jun. 30, 2021	Mar. 31, 2021	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated Other Comprehensive Income (Loss), Net of Tax	$ (24.6)				$ (24.6)		$ (30.9)
Changes in accumulated other comprehensive loss
Other comprehensive income, net of tax, before reclassifications					5.8
Amounts reclassified from AOCL, net of tax benefit of $—, $0.3, $0.1, and $0.4					1.2
Reclassification from AOCI, Current Period, Tax					0.4
Less: noncontrolling interest	(1.6)	$ (5.4)	$ (4.6)	$ 23.2	(7.0)	$ 18.6
Other comprehensive income					6.3
Currency translation adjustments
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated Other Comprehensive Income (Loss), Net of Tax	(1.3)				(1.3)		(1.3)
Changes in accumulated other comprehensive loss
Other comprehensive income, net of tax, before reclassifications					0.0
Amounts reclassified from AOCL, net of tax benefit of $—, $0.3, $0.1, and $0.4					0.0
Reclassification from AOCI, Current Period, Tax					0.0
Other comprehensive income					0.0
Unrealized gains/(losses) on derivative financial instruments
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated Other Comprehensive Income (Loss), Net of Tax	(19.4)				(19.4)		(25.6)
Changes in accumulated other comprehensive loss
Other comprehensive income, net of tax, before reclassifications					5.8
Amounts reclassified from AOCL, net of tax benefit of $—, $0.3, $0.1, and $0.4					1.1
Reclassification from AOCI, Current Period, Tax					0.3
Other comprehensive income					6.2
Accumulated Gain (Loss), Net, Cash Flow Hedge, Noncontrolling Interest [Member]
Changes in accumulated other comprehensive loss
Less: noncontrolling interest					(0.7)
Net actuarial gains/(losses) and prior service costs of defined benefit plans
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated Other Comprehensive Income (Loss), Net of Tax	(3.9)				(3.9)		(4.0)
Changes in accumulated other comprehensive loss
Other comprehensive income, net of tax, before reclassifications					0.0
Amounts reclassified from AOCL, net of tax benefit of $—, $0.3, $0.1, and $0.4					0.1
Reclassification from AOCI, Current Period, Tax					0.1
Other comprehensive income					0.1
Noncontrolling Interest [Member]
Changes in accumulated other comprehensive loss
Less: noncontrolling interest	(0.4)	(0.3)	(0.3)	(0.3)	(0.7)
Accumulated Other Comprehensive Loss
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated Other Comprehensive Income (Loss), Net of Tax	(24.6)				$ (24.6)		$ (30.9)
Changes in accumulated other comprehensive loss
Less: noncontrolling interest	$ (1.2)	$ (5.1)	$ (4.3)	$ 23.5