Summary of Significant Accounting Policies - Fair Value Measurements (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Fair value measured on a recurring basis
Assets
Deferred compensation plan assets	$ 89.5	$ 99.1
Foreign currency forward contracts	0.1	0.0
Total assets measured at fair value	89.6	99.1
Liabilities
Foreign currency forward contracts	0.1	0.1
Total liabilities measured at fair value	0.1	0.1
Quoted Prices in Active Markets for Identical Assets (Level 1) | Fair value measured on a recurring basis
Assets
Deferred compensation plan assets	89.5	99.1
Foreign currency forward contracts	0.0	0.0
Total assets measured at fair value	89.5	99.1
Liabilities
Foreign currency forward contracts	0.0	0.0
Total liabilities measured at fair value	0.0	0.0
Significant Other Observable Inputs (Level 2) | Estimate of fair value measurement
Liabilities
Euro-denominated notes	1,052.9	939.9
Significant Other Observable Inputs (Level 2) | Carrying value
Liabilities
Euro-denominated notes	1,024.6	897.8
Significant Other Observable Inputs (Level 2) | Fair value measured on a recurring basis
Assets
Deferred compensation plan assets	0.0	0.0
Foreign currency forward contracts	0.1	0.0
Total assets measured at fair value	0.1	0.0
Liabilities
Foreign currency forward contracts	0.1	0.1
Total liabilities measured at fair value	0.1	0.1
Significant Unobservable Inputs (Level 3) | Fair value measured on a recurring basis
Assets
Deferred compensation plan assets	0.0	0.0
Foreign currency forward contracts	0.0	0.0
Total assets measured at fair value	0.0	0.0
Liabilities
Foreign currency forward contracts	0.0	0.0
Total liabilities measured at fair value	$ 0.0	$ 0.0