Accumulated Other Comprehensive Loss - Changes in accumulated other comprehensive loss (Details) - USD ($) $ in Millions	3 Months Ended						9 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated Other Comprehensive Income (Loss), Net of Tax	$ (130.5)						$ (130.5)		$ (116.8)
Changes in accumulated other comprehensive loss
Other comprehensive loss, net of tax, before reclassifications							(18.1)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax							5.4
Less: noncontrolling interest	2.7	$ 6.2	$ 3.8	$ (2.1)	$ 0.5	$ (1.9)	12.7	$ (3.5)
Other comprehensive income (loss)							(13.7)
Ending balance	2,459.3	2,529.6	2,565.1	4,643.4	4,671.8	4,834.6	2,459.3	4,643.4
Reclassification from AOCI, Current Period, Tax							1.6
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
Other comprehensive income (loss)							0.0
Reclassification from AOCI, Current Period, Tax							0.0
Unrealized gain/(loss) on derivative financial instruments
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated Other Comprehensive Income (Loss), Net of Tax	(24.5)						(24.5)		(8.3)
Changes in accumulated other comprehensive loss
Other comprehensive loss, net of tax, before reclassifications							(18.1)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax							2.9
Other comprehensive income (loss)							(16.2)
Reclassification from AOCI, Current Period, Tax							0.7
Accumulated Gain (Loss), Net, Cash Flow Hedge, Noncontrolling Interest [Member]
Changes in accumulated other comprehensive loss
Less: noncontrolling interest							(1.0)
Net actuarial gains/(losses) of defined benefit plans
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated Other Comprehensive Income (Loss), Net of Tax	(104.7)						(104.7)		(107.2)
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							2.5
Other comprehensive income (loss)							2.5
Reclassification from AOCI, Current Period, Tax							0.9
Accumulated Other Comprehensive Loss, noncontrolling interest
Changes in accumulated other comprehensive loss
Less: noncontrolling interest	(0.4)	(0.3)	(0.3)	(0.3)	(0.4)	(0.4)	(1.0)
Ending balance	348.7	350.8	350.6	351.1	350.2	352.9	348.7	351.1
Accumulated Other Comprehensive Loss
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated Other Comprehensive Income (Loss), Net of Tax	(130.5)						(130.5)		$ (116.8)
Changes in accumulated other comprehensive loss
Less: noncontrolling interest	3.1	6.5	4.1	(1.8)	0.9	(1.5)
Ending balance	$ (130.5)	$ (127.4)	$ (120.9)	$ (121.1)	$ (122.9)	$ (122.0)	$ (130.5)	$ (121.1)