Benefit Plans and Other Postretirement Benefits, OPEB other (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plan, Assumed Health Care Cost Trend Rates
Health care cost trend rate assumed for next year (as a percent)	7.75%	8.25%
Health care cost trend rate (as a percent)	4.75%
Other Postretirement Benefits
Accumulated other comprehensive income (loss), before tax
Net loss	$ 5.1	$ 5.7
Net prior service cost	0.0	0.0
Net transition asset	0.0	$ 0.0
Expected to be amortized from Accumulated other comprehensive loss over next fiscal year
Net loss that will be amortized from Accumulated other comprehensive loss into net periodic benefit cost over the next fiscal year	0.6
Prior service cost that will be amortized from Accumulated other comprehensive loss into net periodic benefit cost over the next fiscal year	0.0
Net transition asset (obligation) that will be amortized from Accumulated other comprehensive loss into net periodic benefit cost over the next fiscal year	0.0
Other Postretirement Benefits | Minimum
Expected benefit payments
Benefit payments per year, including amounts to be paid out of Company assets and reflecting future expected services, for the next ten years	1.2
Other Postretirement Benefits | Maximum
Expected benefit payments
Benefit payments per year, including amounts to be paid out of Company assets and reflecting future expected services, for the next ten years	$ 1.5