Retirement Benefit Plans (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items]
Pension settlement loss	$ 0.0	$ 0.0	$ 25.7
Defined contribution expense	33.5	28.3	28.0
Defined benefit pension expense	12.5	10.1	35.5
Other postretirement employee benefit expense	0.5	1.4	3.3
Total	46.5	$ 39.8	$ 66.8
Defined Benefit Plan, Estimated Future Employer Contributions in Next Fiscal Year, Under Contractual Obligation	3.5
Minimum [Member]
Defined Benefit Plan Disclosure [Line Items]
Estimated future employer contributions in next fiscal year	15.0
Maximum [Member]
Defined Benefit Plan Disclosure [Line Items]
Estimated future employer contributions in next fiscal year	$ 25.0