Postretirement Benefits Other than Pensions - Additional Information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plan Disclosure [Line Items]
Unrecognized actuarial losses	$ 3.1
Unrecognized actuarial losses, net of tax	2.2
Unrecognized prior service credit	9.8
Unrecognized prior service credit, net of tax	7.0
Postretirement Health Coverage [Member]
Defined Benefit Plan Disclosure [Line Items]
Net gain (loss) recognized in other comprehensive income	(0.2)	$ 0.1	$ (0.3)
Amortization of net loss	0.2	0.3	0.2
Amortization of prior service credit recognized in other comprehensive income	$ 1.3	1.3	$ 1.3
Unrecognized actuarial losses		3.1
Unrecognized actuarial losses, net of tax		1.7
Unrecognized prior service credit		11.1
Unrecognized prior service credit, net of tax		$ 6.1