Fair Value Measurements - Quantitative Information about Level 3 Fair Value (Details) - Option Model - Implied Volatility - Fuel derivatives	Dec. 31, 2019
2020
Quantitative Information About Level 3 [Line Items]
Fair Value Measurement Range, Minimum	13.00%
Fair Value Measurement Range, Maximum	34.00%
2021
Quantitative Information About Level 3 [Line Items]
Fair Value Measurement Range, Minimum	17.00%
Fair Value Measurement Range, Maximum	23.00%
2022
Quantitative Information About Level 3 [Line Items]
Fair Value Measurement Range, Minimum	17.00%
Fair Value Measurement Range, Maximum	19.00%
Beyond 2022
Quantitative Information About Level 3 [Line Items]
Fair Value Measurement Range, Minimum	18.00%
Fair Value Measurement Range, Maximum	19.00%