Segment Information - Schedule of Income Statements and Capital Expenditures By Segment (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2023
Segment Reporting Information [Line Items]
Operating revenues	$ 4,702,755	$ 4,165,187	$ 4,275,357
Operation and maintenance expense	874,910	808,435	743,658
Depreciation and amortization expense	734,745	669,972	604,327
Interest charges	171,678	190,632	137,281
Income tax expense	279,280	192,881	113,779
Other segment items	2,231,330	1,948,355	2,399,957
Net income	1,198,754	1,042,895	885,862
Capital expenditures	3,561,399	2,937,124	2,805,973
Distribution
Segment Reporting Information [Line Items]
Operating revenues	4,422,355	3,912,134	4,096,661
Operation and maintenance expense	644,924	589,864	543,078
Depreciation and amortization expense	543,840	491,982	434,721
Interest charges	99,226	117,086	77,185
Income tax expense	150,961	96,041	60,032
Other segment items	2,239,665	1,948,755	2,404,277
Net income	746,781	671,413	580,397
Capital expenditures	2,662,703	2,249,280	1,927,125
Pipeline and Storage
Segment Reporting Information [Line Items]
Operating revenues	280,400	253,053	178,696
Operation and maintenance expense	229,986	218,571	200,580
Depreciation and amortization expense	190,905	177,990	169,606
Interest charges	72,452	73,546	60,096
Income tax expense	128,319	96,840	53,747
Other segment items	(8,335)	(400)	(4,320)
Net income	451,973	371,482	305,465
Capital expenditures	898,696	687,844	878,848
Intersegment Eliminations
Segment Reporting Information [Line Items]
Operating revenues	(787,942)	(687,983)	(609,507)
Intersegment Eliminations | Distribution
Segment Reporting Information [Line Items]
Operating revenues	(3,042)	(3,007)	(3,029)
Intersegment Eliminations | Pipeline and Storage
Segment Reporting Information [Line Items]
Operating revenues	(784,900)	(684,976)	(606,478)
Operating Segments
Segment Reporting Information [Line Items]
Operating revenues	5,490,697	4,853,170	4,884,864
Operating Segments | Distribution
Segment Reporting Information [Line Items]
Operating revenues	4,425,397	3,915,141	4,099,690
Operating Segments | Pipeline and Storage
Segment Reporting Information [Line Items]
Operating revenues	$ 1,065,300	$ 938,029	$ 785,174