Financial Derivative Instruments - Fuel Hedging (Details) gal in Millions	6 Months Ended
	Jun. 30, 2021 gal
Remainder of 2021
Volume of Fuel Hedging
Fuel Hedged (in gallons)	641
2022
Volume of Fuel Hedging
Fuel Hedged (in gallons)	1,220
2023
Volume of Fuel Hedging
Fuel Hedged (in gallons)	643
Beyond 2023
Volume of Fuel Hedging
Fuel Hedged (in gallons)	106