Debt - Narrative (Details)											1 Months Ended					12 Months Ended
	Oct. 01, 2024 USD ($)	Jun. 21, 2024 USD ($)	Apr. 01, 2024 USD ($)	Mar. 31, 2024 USD ($)	Mar. 28, 2024 USD ($)	Mar. 27, 2024 USD ($)	Oct. 10, 2023 USD ($)	Mar. 23, 2023 USD ($)	Mar. 03, 2023 USD ($)	Oct. 03, 2022 USD ($)	Sep. 30, 2024 USD ($) creditFacility	Sep. 30, 2023 USD ($)	Mar. 31, 2023 USD ($)	Sep. 30, 2022 USD ($)	Feb. 28, 2021 USD ($)	Sep. 30, 2024 USD ($) creditFacility	Sep. 30, 2023 USD ($)	Sep. 30, 2022 USD ($)	Mar. 31, 2021 USD ($)
Debt Instrument [Line Items]
Proceeds from issuance long term debt																$ 1,240,204,000	$ 797,258,000	$ 798,802,000
Offering received																(231,138,000)	(171,145,000)	(197,073,000)
Aggregate natural gas purchases															$ 2,300,000,000
Repayments of long-term debt																$ 0	2,200,000,000	200,000,000
Ratio of total debt to total capitalization maximum																70.00%
Ratio of indebtedness to net capital											0.40					0.40
Minimum
Debt Instrument [Line Items]
Outstanding indebtedness											$ 15,000,000					$ 15,000,000
Maximum
Debt Instrument [Line Items]
Outstanding indebtedness											100,000,000					$ 100,000,000
Texas | Extraordinary Gas Cost | Winter Storm Uri
Debt Instrument [Line Items]
Regulatory asset, proceeds from customer rate relief bonds								$ 2,020,000,000.00					$ 2,020,000,000.00
Senior Notes
Debt Instrument [Line Items]
Debt face amount																			$ 2,200,000,000
Offering received											$ 231,100,000	$ (171,100,000)		$ (197,100,000)
Repayments of long-term debt									$ 2,200,000,000
Unsecured 5.00% Senior Notes, Due October 2054 | Senior Notes | Subsequent Event
Debt Instrument [Line Items]
Debt face amount	$ 650,000,000
Interest rate	5.00%
Effective rate	3.90%
Proceeds from issuance long term debt	$ 638,100,000
Unsecured 5.90% Senior Notes, due October 2033
Debt Instrument [Line Items]
Interest rate											5.90%					5.90%
Unsecured 5.90% Senior Notes, due October 2033 | Senior Notes
Debt Instrument [Line Items]
Debt face amount		$ 325,000,000					$ 400,000,000
Interest rate		5.90%					5.90%
Effective rate		5.17%					4.35%
Proceeds from issuance long term debt		$ 339,000,000
Unsecured 6.20% Senior Notes, due October 2053
Debt Instrument [Line Items]
Interest rate											6.20%					6.20%
Unsecured 6.20% Senior Notes, due October 2053 | Senior Notes
Debt Instrument [Line Items]
Debt face amount							$ 500,000,000
Interest rate							6.20%
Effective rate							5.56%
Unsecured Senior Notes Due 2033 and Unsecured Senior Notes Due 2053 | Senior Notes
Debt Instrument [Line Items]
Proceeds from issuance of debt							$ 889,400,000
Unsecured 5.75% Senior Notes, due October 2052
Debt Instrument [Line Items]
Interest rate											5.75%					5.75%
Unsecured 5.75% Senior Notes, due October 2052 | Senior Notes
Debt Instrument [Line Items]
Debt face amount										$ 500,000,000
Interest rate										5.75%
Effective rate										4.50%
Unsecured 5.45% Senior Notes, due October 2032
Debt Instrument [Line Items]
Interest rate											5.45%					5.45%
Unsecured 5.45% Senior Notes, due October 2032 | Senior Notes
Debt Instrument [Line Items]
Debt face amount										$ 300,000,000
Interest rate										5.45%
Effective rate										5.57%
Unsecured Senior Notes Due 2032 and Unsecured Senior Notes Due 2052 | Senior Notes
Debt Instrument [Line Items]
Proceeds from issuance of debt										$ 789,400,000
Unsecured Senior Notes Due 2052 | Senior Notes
Debt Instrument [Line Items]
Debt face amount														$ 500,000,000				$ 500,000,000
Unsecured Senior Term Loan Due 2023 | Unsecured Debt | Line of Credit
Debt Instrument [Line Items]
Debt face amount									$ 2,020,000,000.00
Five Year Unsecured Revolving Credit Agreement, Maturing On March 28, 2029 | Minimum | Base Rate
Debt Instrument [Line Items]
Basis spread percent																0.00%
Five Year Unsecured Revolving Credit Agreement, Maturing On March 28, 2029 | Minimum | Secured Overnight Financing Rate (SOFR)
Debt Instrument [Line Items]
Basis spread percent																75.00%
Five Year Unsecured Revolving Credit Agreement, Maturing On March 28, 2029 | Maximum | Base Rate
Debt Instrument [Line Items]
Basis spread percent																25.00%
Five Year Unsecured Revolving Credit Agreement, Maturing On March 28, 2029 | Maximum | Secured Overnight Financing Rate (SOFR)
Debt Instrument [Line Items]
Basis spread percent																125.00%
Five Year Unsecured Revolving Credit Agreement, Maturing On March 28, 2029 | Commercial Paper
Debt Instrument [Line Items]
Maximum borrowing capacity					$ 1,500,000,000						$ 1,500,000,000					$ 1,500,000,000
Debt term					5 years
Credit facility, accordion feature					$ 250,000,000
Loan increase potential					1,750,000,000
Five Year Unsecured Revolving Credit Agreement, Maturing On March 28, 2029 | Revolving Credit Facility
Debt Instrument [Line Items]
Maximum borrowing capacity											$ 3,100,000,000					$ 3,100,000,000
Number of credit facilities | creditFacility											4					4
Five Year Unsecured Revolving Credit Agreement
Debt Instrument [Line Items]
Commercial paper											$ 0	241,900,000				$ 0	241,900,000
Five Year Unsecured Revolving Credit Agreement | Commercial Paper
Debt Instrument [Line Items]
Maximum borrowing capacity						$ 1,500,000,000
Debt term						5 years
$900 Million Revolving Credit Facility | Revolving Credit Facility
Debt Instrument [Line Items]
Maximum borrowing capacity						$ 900,000,000
Debt term						3 years
Line of credit borrowings outstanding											0	0				0	0
$1.5 Billion Revolving Credit Facility | Revolving Credit Facility
Debt Instrument [Line Items]
Maximum borrowing capacity					$ 1,500,000,000
Debt term					3 years
Credit facility, accordion feature					$ 250,000,000
Loan increase potential					$ 1,750,000,000
Line of credit borrowings outstanding											0	0				$ 0	0
$1.5 Billion Revolving Credit Facility | Revolving Credit Facility | Minimum | Base Rate
Debt Instrument [Line Items]
Basis spread percent																0.00%
$1.5 Billion Revolving Credit Facility | Revolving Credit Facility | Minimum | Secured Overnight Financing Rate (SOFR)
Debt Instrument [Line Items]
Basis spread percent																75.00%
$1.5 Billion Revolving Credit Facility | Revolving Credit Facility | Maximum | Base Rate
Debt Instrument [Line Items]
Basis spread percent																25.00%
$1.5 Billion Revolving Credit Facility | Revolving Credit Facility | Maximum | Secured Overnight Financing Rate (SOFR)
Debt Instrument [Line Items]
Basis spread percent																125.00%
$50 Million Bank Loan Agreement | Line of Credit
Debt Instrument [Line Items]
Maximum borrowing capacity			$ 50,000,000
Debt term			364 days
Line of credit borrowings outstanding											0	$ 0				$ 0	$ 0
$50 Million Revolving Credit Facility | Revolving Credit Facility
Debt Instrument [Line Items]
Maximum borrowing capacity				$ 50,000,000
Debt term				364 days
Line of credit borrowings outstanding											0					0
Remaining borrowing capacity											$ 44,400,000					$ 44,400,000