Accumulated Other Comprehensive Loss - Changes in accumulated other comprehensive loss (Details) - USD ($) $ in Millions	3 Months Ended				6 Months Ended
	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated Other Comprehensive Income (Loss), Net of Tax	$ (172.3)				$ (172.3)		$ (153.1)
Changes in accumulated other comprehensive loss
Other comprehensive loss, net of tax, before reclassifications					(27.3)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax					8.7
Reclassification from AOCI, Current Period, Tax					2.5
Less: noncontrolling interest	(4.6)	$ 23.2	$ 6.2	$ 3.8	18.6	$ 10.0
Other comprehensive income (loss)					(19.2)
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 loss, net of tax, before reclassifications					0.0
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax					0.0
Reclassification from AOCI, Current Period, Tax					0.0
Other comprehensive income (loss)					0.0
Unrealized gain/(loss) on derivative financial instruments
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated Other Comprehensive Income (Loss), Net of Tax	(39.9)				(39.9)		(17.9)
Changes in accumulated other comprehensive loss
Other comprehensive loss, net of tax, before reclassifications					(27.3)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax					5.9
Reclassification from AOCI, Current Period, Tax					1.7
Other comprehensive income (loss)					(22.0)
Accumulated Gain (Loss), Net, Cash Flow Hedge, Noncontrolling Interest [Member]
Changes in accumulated other comprehensive loss
Less: noncontrolling interest					(0.6)
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	(131.1)				(131.1)		(133.9)
Changes in accumulated other comprehensive loss
Other comprehensive loss, net of tax, before reclassifications					0.0
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax					2.8
Reclassification from AOCI, Current Period, Tax					0.8
Other comprehensive income (loss)					2.8
Noncontrolling Interest [Member]
Changes in accumulated other comprehensive loss
Less: noncontrolling interest	(0.3)	(0.3)	(0.3)	(0.3)	(0.6)
Accumulated Other Comprehensive Loss
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated Other Comprehensive Income (Loss), Net of Tax	(172.3)				$ (172.3)		$ (153.1)
Changes in accumulated other comprehensive loss
Less: noncontrolling interest	$ (4.3)	$ 23.5	$ 6.5	$ 4.1