Summary of Significant Accounting Policies - Fair Value Disclosures (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
W.A. Sanders Coldenhove Holding B.V. | Insurance Contracts Acquired in Business Combination
Defined Benefit Plan Disclosure [Line Items]
Transfers into/ (out of) Level 3	$ 46.8
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	400.4	$ 318.1	$ 308.3
Pension Benefits | W.A. Sanders Coldenhove Holding B.V.
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	46.8
Cash and cash equivalents | Level 1 | Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1.6	1.5
U.S. and Non-U.S. Equities | Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets measured at NAV	123.2	112.2
U.S. and Non-U.S. Fixed Income Securities | Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets measured at NAV	199.0	181.1
Hedge Funds | Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets measured at NAV	$ 28.2	$ 23.3