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Financial Derivative Instruments - Fair Values of Fuel Derivatives Amounts Posted as Collateral (Details)
$ in Millions
Sep. 30, 2024
USD ($)
If credit rating is investment grade, fair value of fuel derivative level at which:  
Letter of credit substitution percentage 100.00%
Cash collateral percentage 100.00%
Fuel derivative contracts  
Schedule Of Fair Values Of Fuel Derivatives Amounts Posted As Collateral And Collateral Posting Thresholds [Line Items]  
Fair value of fuel derivatives $ 132
Cash collateral held from CP 22
Fuel derivative contracts | A  
Schedule Of Fair Values Of Fuel Derivatives Amounts Posted As Collateral And Collateral Posting Thresholds [Line Items]  
Fair value of fuel derivatives 27
Cash collateral held from CP 22
Fuel derivative contracts | A | Minimum  
If credit rating is investment grade, fair value of fuel derivative level at which:  
Cash is provided to CP (100)
Cash is received from CP 0
Fuel derivative contracts | B  
Schedule Of Fair Values Of Fuel Derivatives Amounts Posted As Collateral And Collateral Posting Thresholds [Line Items]  
Fair value of fuel derivatives 15
Cash collateral held from CP 0
Fuel derivative contracts | B | Minimum  
If credit rating is investment grade, fair value of fuel derivative level at which:  
Cash is provided to CP (50)
Cash is received from CP 150
Fuel derivative contracts | C  
Schedule Of Fair Values Of Fuel Derivatives Amounts Posted As Collateral And Collateral Posting Thresholds [Line Items]  
Fair value of fuel derivatives 22
Cash collateral held from CP 0
Fuel derivative contracts | C | Minimum  
If credit rating is investment grade, fair value of fuel derivative level at which:  
Cash is provided to CP (75)
Cash is received from CP 250
Fuel derivative contracts | D  
Schedule Of Fair Values Of Fuel Derivatives Amounts Posted As Collateral And Collateral Posting Thresholds [Line Items]  
Fair value of fuel derivatives 11
Cash collateral held from CP 0
Fuel derivative contracts | D | Minimum  
If credit rating is investment grade, fair value of fuel derivative level at which:  
Cash is provided to CP (125)
Cash is received from CP 125
Fuel derivative contracts | E  
Schedule Of Fair Values Of Fuel Derivatives Amounts Posted As Collateral And Collateral Posting Thresholds [Line Items]  
Fair value of fuel derivatives 20
Cash collateral held from CP 0
Fuel derivative contracts | E | Minimum  
If credit rating is investment grade, fair value of fuel derivative level at which:  
Cash is provided to CP (40)
Cash is received from CP 100
Fuel derivative contracts | F  
Schedule Of Fair Values Of Fuel Derivatives Amounts Posted As Collateral And Collateral Posting Thresholds [Line Items]  
Fair value of fuel derivatives 8
Cash collateral held from CP 0
Fuel derivative contracts | F | Minimum  
If credit rating is investment grade, fair value of fuel derivative level at which:  
Cash is provided to CP (65)
Cash is received from CP 70
Fuel derivative contracts | G  
Schedule Of Fair Values Of Fuel Derivatives Amounts Posted As Collateral And Collateral Posting Thresholds [Line Items]  
Fair value of fuel derivatives 15
Cash collateral held from CP 0
Fuel derivative contracts | G | Minimum  
If credit rating is investment grade, fair value of fuel derivative level at which:  
Cash is provided to CP (100)
Cash is received from CP 100
Fuel derivative contracts | H  
Schedule Of Fair Values Of Fuel Derivatives Amounts Posted As Collateral And Collateral Posting Thresholds [Line Items]  
Fair value of fuel derivatives 10
Cash collateral held from CP 0
Fuel derivative contracts | H | Minimum  
If credit rating is investment grade, fair value of fuel derivative level at which:  
Cash is provided to CP (100)
Cash is received from CP 100
Fuel derivative contracts | I  
Schedule Of Fair Values Of Fuel Derivatives Amounts Posted As Collateral And Collateral Posting Thresholds [Line Items]  
Fair value of fuel derivatives 4
Cash collateral held from CP $ 0