Financial Derivative Instruments - Fuel Hedging (Details) gal in Millions	Dec. 31, 2019 gal	[1]
2020
Volume of Fuel Hedging
Fuel Hedged (in gallons)	1,301
2021
Volume of Fuel Hedging
Fuel Hedged (in gallons)	1,169
2022
Volume of Fuel Hedging
Fuel Hedged (in gallons)	603
Beyond 2022
Volume of Fuel Hedging
Fuel Hedged (in gallons)	32

[1] Due to the types of derivatives utilized by the Company and different price levels of those contracts, these volumes represent the maximum economic hedge in place and may vary significantly as market prices fluctuate.