Pensions and Other Postretirement Benefits - Additional Information (Details) - USD ($)	3 Months Ended			9 Months Ended		12 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2020	Dec. 31, 2019
Defined Benefit Plan Disclosure [Line Items]
Transfer of remaining pension benefit obligation to annuity			$ 713,000,000
Non-cash settlement charge			$ 152,500,000
Increase in multi-employer plan withdrawal obligation	$ 12,200,000	$ 12,200,000
Estimated liability for withdrawal from multi-employer plans	$ 42,100,000			$ 42,100,000
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Company's contributions to its pension plans				16,000,000.0	$ 8,200,000		$ 11,300,000
Pension Benefits | Minimum | Forecast
Defined Benefit Plan Disclosure [Line Items]
Company's contributions to its pension plans						$ 15,000,000
Pension Benefits | Maximum | Forecast
Defined Benefit Plan Disclosure [Line Items]
Company's contributions to its pension plans						20,000,000
Postretirement Health Care Benefits
Defined Benefit Plan Disclosure [Line Items]
Benefit payments				$ 1,500,000	$ 2,200,000		$ 1,200,000
Postretirement Health Care Benefits | Forecast
Defined Benefit Plan Disclosure [Line Items]
Benefit payments						$ 3,000,000