Fair Value Measurements and Derivative Instruments (Fuel Price Risk) (Details) - Fuel Price Risk $ in Millions	12 Months Ended
	Dec. 31, 2021 USD ($) t T	Dec. 31, 2020 USD ($) t T
Derivative instruments disclosure
Discontinued cash flow hedge, nonmonetary amount | T	200,000	600,000
Estimated unrealized net gains (losses) associated with cash flow hedges pertaining to fuel swap agreements expected to be reclassified to earnings from other accumulated comprehensive income (loss) | $	$ 23.8	$ (13.1)
Other income (expense)
Derivative instruments disclosure
Discontinued cash flow hedge, reclassification loss | $	$ 0.7	$ 104.4
2022
Derivative instruments disclosure
Fuel Swap Agreements (metric tons) | T	821,850,000	389,650,000
Percentage of projected requirements	54.00%	23.00%
2022 | Not Designated as Hedging Instrument
Derivative instruments disclosure
Discontinued cash flow hedge, nonmonetary amount | t	115,950
Fuel Swap Agreements (metric tons) | t	231,900,000	14,650,000
Nonmonetary amount since inception | t	115,950
2023
Derivative instruments disclosure
Fuel Swap Agreements (metric tons) | T	249,050,000	82,400,000
Percentage of projected requirements	15.00%	5.00%