Employee Retirement Plans and Postretirement Benefits Amortization Amounts Expected (Details) $ in Millions	12 Months Ended
	Dec. 31, 2017 USD ($)
Defined Benefit Plan Disclosure [Line Items]
Amortization of net prior service cost (gain)	$ 0.6
Amortization of actuarial net loss (gain)	6.1
Pension
Defined Benefit Plan Disclosure [Line Items]
Amortization of net prior service cost (gain)	0.7
Amortization of actuarial net loss (gain)	7.8
OPEB
Defined Benefit Plan Disclosure [Line Items]
Amortization of net prior service cost (gain)	(0.1)
Amortization of actuarial net loss (gain)	$ (1.7)