Variable Interest Entity - Schedule of Consolidated Statement of Comprehensive Income (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Mar. 31, 2024	Mar. 31, 2023
Variable Interest Entity [Line Items]
Operating revenues	$ 1,647,227	$ 1,540,973	$ 2,805,694	$ 3,024,982
Operation and maintenance expense	(199,899)	(194,716)	(366,244)	(379,732)
Amortization expense	(165,087)	(148,317)	(329,695)	(294,337)
Interest expense, net	(55,442)	(37,370)	(107,317)	(74,130)
Income before income taxes	512,235	$ 402,674	877,351	$ 708,291
Variable Interest Entity, Primary Beneficiary | AEK
Variable Interest Entity [Line Items]
Operating revenues	3,469		6,802
Operation and maintenance expense	(224)		(224)
Amortization expense	(2,103)		(4,269)
Interest expense, net	(1,142)		(2,309)
Income before income taxes	$ 0		$ 0