Accumulated Other Comprehensive Loss - Changes in accumulated other comprehensive loss (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Accumulated Other Comprehensive Income (Loss) [Line Items]
Reclassification from AOCI, Current Period, Tax	$ (1.1)	$ (2.2)
Before-tax reclassification of net actuarial gains/(losses)	(4.8)	(4.9)	$ (5.1)
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	4,858.0	4,311.1	4,048.7
Other comprehensive loss, net of tax, before reclassifications	(19.1)	4.0
Amounts reclassified from accumulated other comprehensive loss, net of tax	5.9	7.3
Less: noncontrolling interest	13.2	(11.3)	(5.0)
Other comprehensive loss	(14.6)	8.7
Ending balance	2,562.0	4,858.0	4,311.1
Stockholders' Equity Note, Spinoff Transaction	(1,732.2)
Currency translation adjustments
Accumulated Other Comprehensive Income (Loss) [Line Items]
Reclassification from AOCI, Current Period, Tax	0.0	0.0
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(22.4)	(23.7)
Other comprehensive loss, net of tax, before reclassifications	0.0	1.3
Amounts reclassified from accumulated other comprehensive loss, net of tax	0.0	0.0
Other comprehensive loss	0.0	1.3
Ending balance	(1.3)	(22.4)	(23.7)
Stockholders' Equity Note, Spinoff Transaction	21.3
Cumulative Effect of New Accounting Principle in Period of Adoption	(0.2)
Currency translation adjustments attributable to noncontrolling interest
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Less: noncontrolling interest	0.0	0.0
Unrealized loss on derivative financial instruments
Accumulated Other Comprehensive Income (Loss) [Line Items]
Reclassification from AOCI, Current Period, Tax	0.0	(0.7)
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	0.3	(0.1)
Other comprehensive loss, net of tax, before reclassifications	(9.6)	(0.9)
Amounts reclassified from accumulated other comprehensive loss, net of tax	2.3	3.9
Other comprehensive loss	(8.7)	0.4
Ending balance	(8.3)	0.3	(0.1)
Cumulative Effect of New Accounting Principle in Period of Adoption	0.1
Unrealized loss on derivative financial instruments attributable to noncontrolling interest
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Less: noncontrolling interest	(1.4)	(2.6)
Net actuarial gains/(losses) of defined benefit plans
Accumulated Other Comprehensive Income (Loss) [Line Items]
Reclassification from AOCI, Current Period, Tax	(1.1)	(1.5)
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(82.7)	(89.7)
Other comprehensive loss, net of tax, before reclassifications	(9.5)	3.6
Amounts reclassified from accumulated other comprehensive loss, net of tax	3.6	3.4
Other comprehensive loss	(5.9)	7.0
Ending balance	(107.2)	(82.7)	(89.7)
Cumulative Effect of New Accounting Principle in Period of Adoption	(18.6)
Net actuarial gains/(losses) of defined benefit plans attributable to noncontrolling interest
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Less: noncontrolling interest	0.0	0.0
Accumulated Other Comprehensive Loss
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(104.8)	(113.5)	(115.4)
Less: noncontrolling interest	14.6	(8.7)	(1.9)
Ending balance	(116.8)	(104.8)	(113.5)
Stockholders' Equity Note, Spinoff Transaction	21.3
Cumulative Effect of New Accounting Principle in Period of Adoption	(18.7)
Accumulated Other Comprehensive Loss attributable to noncontrolling interest
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	356.9	392.6	394.8
Less: noncontrolling interest	(1.4)	(2.6)	(3.1)
Ending balance	$ 351.2	$ 356.9	$ 392.6