Other Postretirement Benefit Plans - Narrative (Details) - USD ($)	1 Months Ended	3 Months Ended					12 Months Ended
	Jan. 31, 2021	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Dec. 31, 2019	Sep. 30, 2019	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Recognition of net actuarial losses (gains)		$ (21,600,000)	$ (11,900,000)	$ (8,800,000)	$ (21,100,000)	$ (16,900,000)		$ (18,500,000)	$ 4,100,000	$ (12,800,000)
Accrued postretirement liability
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Recognition of net actuarial losses (gains)								$ (1,400,000)	$ 18,000,000.0	$ 16,700,000
Discount rate		2.62%			3.43%			2.62%	3.43%	4.30%	3.57%
Actuarial losses (gains)								$ 1,800,000	$ (14,400,000)
Plan amendments						$ 92,800,000		$ 3,100,000	$ 92,800,000
Discount rate related to the postretirement plans								3.43%		3.57%
Expected long-term return on plan assets								3.00%	4.85%	4.50%
Current liabilities		$ 5,200,000			$ 3,800,000			$ 5,200,000	$ 3,800,000
Weighted average annual rate of increase in per capita cost for medical benefits								5.50%
Weighted average annual rate of increase in per capita cost for medical benefits declining gradually								5.00%
Weighted average annual rate of increase for prescription drug benefits and HMO benefits								7.25%
Effect of one percentage point increase on service and interest cost components								$ 100,000
Effect of one percentage point increase on accumulated postretirement benefit obligation								1,800,000
Effect of one percentage point decrease on service and interest cost components								(100,000)
Effect of one percentage point decrease on accumulated postretirement benefit obligation								(1,600,000)
Net periodic benefit cost								$ 50,000,000
Accrued postretirement liability | Subsequent Event
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net periodic benefit cost	$ 11,100,000
Accrued postretirement liability | Forecast
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Discount rate related to the postretirement plans							2.62%
Health Maintenance Organization (HMO) | Accrued postretirement liability
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Weighted average annual rate of increase in per capita for prescription drug benefits and HMO benefits declining								5.00%
Return on Plan Assets vs. Expectation | Accrued postretirement liability
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Recognition of net actuarial losses (gains)								$ 400,000	3,600,000	$ 4,000,000.0
Actuarial losses (gains)								2,000,000.0
Other Valuation Assumptions | Accrued postretirement liability
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Recognition of net actuarial losses (gains)								$ 100,000	$ 5,200,000	$ 300,000
Discount Rate In Basis Points | Accrued postretirement liability
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Decrease to discount rate								(0.0081)	(0.0087)	73
Discount Rate In Dollars | Accrued postretirement liability
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Recognition of net actuarial losses (gains)								$ (3,900,000)	$ (13,500,000)	$ 10,600,000
Change in Assumptions for Defined Benefit Plans | Accrued postretirement liability
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Recognition of net actuarial losses (gains)									$ 22,700,000
Employee Opt-Out Program | Accrued postretirement liability
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Recognition of net actuarial losses (gains)										$ 10,400,000