Financial Instruments - Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Jan. 01, 2018
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at the beginning of the period		$ 2,597.4	$ 2,528.3	$ 2,466.9
Adoption of accounting standard	[1]				$ 6.5
Other comprehensive income (loss) before reclassifications		(6.8)	(35.0)
Amounts reclassified from accumulated other comprehensive income (loss)		4.2	5.0
Income tax benefit		0.6	0.1
Other comprehensive (loss) income		(2.0)	(29.9)	36.5
Balance at the end of the period		2,642.8	2,597.4	2,528.3
Accrued post-retirement benefit liability
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at the beginning of the period		(38.5)	(31.6)
Adoption of accounting standard					(6.5)
Other comprehensive income (loss) before reclassifications		(6.0)	(5.1)
Amounts reclassified from accumulated other comprehensive income (loss)		3.4	4.6
Income tax benefit		0.6	0.1
Other comprehensive (loss) income		(2.0)	(0.4)
Balance at the end of the period		(40.5)	(38.5)	(31.6)
Foreign currency translation
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at the beginning of the period		(80.4)	(50.1)
Other comprehensive income (loss) before reclassifications		(2.1)	(30.3)
Other comprehensive (loss) income		(2.1)	(30.3)
Balance at the end of the period		(82.5)	(80.4)	(50.1)
Foreign currency forward contracts
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at the beginning of the period		(3.2)	(4.0)
Other comprehensive income (loss) before reclassifications		1.3	0.4
Amounts reclassified from accumulated other comprehensive income (loss)		0.8	0.4
Income tax benefit		0.0	0.0
Other comprehensive (loss) income		2.1	0.8
Balance at the end of the period		(1.1)	(3.2)	(4.0)
Accumulated Other Comprehensive Income (loss).
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at the beginning of the period		(122.1)	(85.7)	(122.2)
Adoption of accounting standard	[1]				$ (6.5)
Other comprehensive (loss) income		(2.0)	(29.9)	36.5
Balance at the end of the period		$ (124.1)	$ (122.1)	$ (85.7)

[1] Refer to Note 1 for further information regarding new accounting standards adopted.