Accumulated Other Comprehensive Loss - Changes in accumulated other comprehensive loss (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Changes in accumulated other comprehensive loss
Beginning balance	$ 2,562.0	$ 4,858.0
Other comprehensive loss, net of tax, before reclassifications	(5.5)
Amounts reclassified from accumulated other comprehensive loss, net of tax benefit of $-, $0.3, $0.3, and $0.6	1.7
Less: noncontrolling interest	3.8	(1.9)
Other comprehensive income (loss)	(4.1)
Ending balance	2,565.1	4,834.6
Amounts reclassified from accumulated other comprehensive loss, tax expense (benefit)	(0.6)
Currency translation adjustments
Changes in accumulated other comprehensive loss
Beginning balance	(1.3)
Other comprehensive loss, net of tax, before reclassifications	0.0
Amounts reclassified from accumulated other comprehensive loss, net of tax benefit of $-, $0.3, $0.3, and $0.6	0.0
Other comprehensive income (loss)	0.0
Ending balance	(1.3)
Amounts reclassified from accumulated other comprehensive loss, tax expense (benefit)	0.0
Unrealized gain/(loss) on derivative financial instruments
Changes in accumulated other comprehensive loss
Beginning balance	(8.3)
Other comprehensive loss, net of tax, before reclassifications	(5.5)
Amounts reclassified from accumulated other comprehensive loss, net of tax benefit of $-, $0.3, $0.3, and $0.6	0.9
Other comprehensive income (loss)	(4.9)
Ending balance	(13.2)
Amounts reclassified from accumulated other comprehensive loss, tax expense (benefit)	(0.3)
Accumulated Gain (Loss), Net, Cash Flow Hedge, Noncontrolling Interest [Member]
Changes in accumulated other comprehensive loss
Less: noncontrolling interest	(0.3)
Net actuarial gains/(losses) of defined benefit plans
Changes in accumulated other comprehensive loss
Beginning balance	(107.2)
Other comprehensive loss, net of tax, before reclassifications	0.0
Amounts reclassified from accumulated other comprehensive loss, net of tax benefit of $-, $0.3, $0.3, and $0.6	0.8
Other comprehensive income (loss)	0.8
Ending balance	(106.4)
Amounts reclassified from accumulated other comprehensive loss, tax expense (benefit)	(0.3)
Accumulated Other Comprehensive Loss, noncontrolling interest
Changes in accumulated other comprehensive loss
Beginning balance	351.2	356.9
Less: noncontrolling interest	(0.3)	(0.4)
Ending balance	350.6	352.9
Accumulated Other Comprehensive Loss
Changes in accumulated other comprehensive loss
Beginning balance	(116.8)	(104.8)
Less: noncontrolling interest	4.1	(1.5)
Ending balance	$ (120.9)	$ (122.0)