Postretirement Benefits Other Than Pensions - Narrative (Details) $ in Millions	12 Months Ended
	Dec. 31, 2019 USD ($) employees	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Other Postretirement Benefit Plan, Defined Benefit
Defined Benefit Plan Disclosure [Line Items]
Number of retired employees covered | employees	650
Number of active employees covered | employees	525
Pre-tax reduction to its accumulated postretirement benefit obligation	$ 0.0	$ 0.0	$ (1.3)	$ 11.0
Effect of one percentage point increase on accumulated postretirement benefit obligation	0.6	$ 0.8
Amounts that will be amortized from AOCI in next fiscal Year	3.3
Estimated future employer contributions in next fiscal year	$ 1.3
Medical Benefits
Defined Benefit Plan Disclosure [Line Items]
Health care cost trend rate assumed for next fiscal year	7.50%	7.50%
Health care cost trend rate assumed for future years	4.80%	4.80%
Prescription Drug Benefits
Defined Benefit Plan Disclosure [Line Items]
Health care cost trend rate assumed for next fiscal year	10.00%	10.00%
Health care cost trend rate assumed for future years	4.80%	4.80%