Pensions and Other Postretirement Benefits - Additional Information (Details) - USD ($) $ in Millions		3 Months Ended		6 Months Ended		12 Months Ended
	Jan. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2020	Dec. 31, 2019
Defined Benefit Plan Disclosure [Line Items]
Transfer of remaining pension benefit obligation to annuity	$ 713.0
Non-cash settlement charge			$ 152.5
Increase in multi-employer plan withdrawal obligation		$ 12.2
Estimated liability for withdrawal from multi-employer plans		$ 42.5		$ 42.5
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Company's contributions to its pension plans				1.1	$ 1.1		$ 11.3
Pension Benefits | Minimum | Forecast
Defined Benefit Plan Disclosure [Line Items]
Company's contributions to its pension plans						$ 10.0
Pension Benefits | Maximum | Forecast
Defined Benefit Plan Disclosure [Line Items]
Company's contributions to its pension plans						20.0
Postretirement Health Care Benefits
Defined Benefit Plan Disclosure [Line Items]
Benefit payments				$ 1.0	$ 1.2		$ 1.2
Postretirement Health Care Benefits | Forecast
Defined Benefit Plan Disclosure [Line Items]
Benefit payments						$ 3.0