Employee Benefit Plans and Other Postretirement Benefits - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plan Disclosure [Line Items]
Retirement age threshold		55 years
Postretirement benefits eligibility, years of service requirement		10 years
Period over which asset gain (losses) are amortized		5 years
Company contributions		$ 21,900,000	$ 20,100,000	$ 19,000,000.0
Pension and SERPA Benefits
Defined Benefit Plan Disclosure [Line Items]
Accumulated benefit obligation		$ 2,120,000,000	$ 1,900,000,000
Expected return on plan assets		7.10%	7.25%	7.25%
Pension Plan Assets
Defined Benefit Plan Disclosure [Line Items]
Investment in company common stock - shares		1,273,592	1,273,592
Investment in company common stock - value		$ 47,400,000	$ 43,500,000
Company contributions		$ 0
Pension Plan Assets | Scenario, Forecast
Defined Benefit Plan Disclosure [Line Items]
Expected return on plan assets	6.70%
Pension Plan Assets | Equity Securities
Defined Benefit Plan Disclosure [Line Items]
Target plan asset allocation		56.00%
Pension Plan Assets | Fixed Income Securities and Cash and Cash Equivalents
Defined Benefit Plan Disclosure [Line Items]
Target plan asset allocation		44.00%
Postretirement Health Coverage
Defined Benefit Plan Disclosure [Line Items]
Expected return on plan assets		7.25%	7.25%	7.25%
Company contributions		$ 0
Postretirement Health Coverage | Scenario, Forecast
Defined Benefit Plan Disclosure [Line Items]
Expected return on plan assets	7.00%
Postretirement Health Coverage | Equity Securities
Defined Benefit Plan Disclosure [Line Items]
Target plan asset allocation		69.00%
Postretirement Health Coverage | Fixed Income Securities and Cash and Cash Equivalents
Defined Benefit Plan Disclosure [Line Items]
Target plan asset allocation		31.00%