Employee Benefit Plans - Summary of the Sensitivity of Retirement Obligations and Retirement Benefit Costs of Plans to Changes in the Key Assumptions (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Pension Plans
Estimated increase (decrease) in 2017 pension cost
0.50% increase in discount rate	$ (0.9)
0.50% decrease in discount rate	0.9
0.50% increase in long-term return on assets	(0.8)
0.50% decrease in long-term return on assets	0.8
Estimated increase (decrease) in Projected Benefit Obligation for the year ended December 31, 2016
0.50% increase in discount rate		$ (15.0)
0.50% decrease in discount rate		16.2
Postretirement Health and Other
Estimated increase (decrease) in 2017 pension cost
0.50% increase in discount rate	(0.1)
0.50% decrease in discount rate	0.1
1% increase in medical trend rates	0.3
1% decrease in medical trend rates	$ (0.3)
Estimated increase (decrease) in Projected Benefit Obligation for the year ended December 31, 2016
0.50% increase in discount rate		(0.9)
0.50% decrease in discount rate		0.9
1% increase in medical trend rates		1.4
1% decrease in medical trend rates		$ (1.3)