Debt - Narrative (Details)									1 Months Ended				12 Months Ended
	Oct. 10, 2023 USD ($)	Apr. 01, 2023 USD ($)	Mar. 31, 2023 USD ($)	Mar. 23, 2023 USD ($)	Mar. 03, 2023 USD ($)	Oct. 03, 2022 USD ($)	Jan. 18, 2022 USD ($)	Oct. 01, 2021 USD ($)	Sep. 30, 2023 USD ($) creditFacility	Sep. 30, 2022 USD ($)	Sep. 30, 2021 USD ($)	Feb. 28, 2021 USD ($)	Sep. 30, 2023 USD ($) creditFacility	Sep. 30, 2022 USD ($)	Sep. 30, 2021 USD ($)	Jan. 14, 2022 USD ($)	Mar. 31, 2021 USD ($)
Debt Instrument [Line Items]
Proceeds from hedge													$ 171,145,000	$ 197,073,000	$ 62,159,000
Long term debt									$ 6,560,000,000				6,560,000,000
Aggregate natural gas purchases												$ 2,300,000,000
Repayments of long-term debt													$ 2,200,000,000	200,000,000	$ 0
Ratio of total debt to total capitalization maximum													70.00%
Ratio of indebtedness to net capital									0.40				0.40
Texas | Extraordinary Gas Cost | Winter Storm Uri
Debt Instrument [Line Items]
Regulatory asset, proceeds from customer rate relief bonds				$ 2,020,000,000.00
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
Senior Notes
Debt Instrument [Line Items]
Debt face amount																	$ 2,200,000,000
Proceeds from hedge									171,100,000	$ 197,100,000	$ 62,200,000
Repayments of long-term debt					$ 2,200,000,000
Unsecured Senior Notes Due 2053 | Senior Notes | Subsequent Event
Debt Instrument [Line Items]
Debt face amount	$ 500,000,000
Interest rate	6.20%
Effective rate	5.56%
Unsecured Senior Notes Due 2033 | Senior Notes | Subsequent Event
Debt Instrument [Line Items]
Debt face amount	$ 400,000,000
Interest rate	5.90%
Effective rate	4.35%
Unsecured Senior Notes Due 2033 and Unsecured Senior Notes Due 2053 | Senior Notes | Subsequent Event
Debt Instrument [Line Items]
Proceeds from issuance of debt	$ 889,200,000
Unsecured Senior Notes Due 2052 | Senior Notes
Debt Instrument [Line Items]
Debt face amount						$ 500,000,000			$ 500,000,000				$ 500,000,000
Interest rate						5.75%
Effective rate						4.50%
Unsecured Senior Notes Due 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 2029
Debt Instrument [Line Items]
Interest rate									2.625%				2.625%
Long term debt									$ 500,000,000	500,000,000			$ 500,000,000	500,000,000
Unsecured Senior Notes Due 2029 | Senior Notes
Debt Instrument [Line Items]
Debt face amount																$ 200,000,000
Interest rate																2.625%
Effective rate																2.54%
Long term debt																$ 200,800,000
Floating-rate Term Loan | Senior Notes
Debt Instrument [Line Items]
Repayments of debt							$ 200,000,000
Unsecured Senior Notes Due 2052
Debt Instrument [Line Items]
Interest rate									2.85%				2.85%
Long term debt									$ 600,000,000	600,000,000			$ 600,000,000	600,000,000
Unsecured Senior Notes Due 2052 | Senior Notes
Debt Instrument [Line Items]
Debt face amount								$ 600,000,000
Interest rate								2.85%
Effective rate								2.58%
Proceeds from issuance of debt								$ 589,800,000
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
Debt Instrument [Line Items]
Commercial paper									241,900,000	185,000,000			241,900,000	185,000,000
Five Year Unsecured Revolving Credit Agreement | Commercial Paper
Debt Instrument [Line Items]
Maximum borrowing capacity									1,500,000,000				$ 1,500,000,000
Debt term													5 years
Credit facility, accordion feature									250,000,000				$ 250,000,000
Loan increase potential									$ 1,750,000,000				$ 1,750,000,000
Weighted average interest rate									5.46%				5.46%
Five Year Unsecured Revolving Credit Agreement | Revolving Credit Facility
Debt Instrument [Line Items]
Maximum borrowing capacity									$ 2,500,000,000				$ 2,500,000,000
Number of credit facilities | creditFacility									4				4
Five Year Unsecured Revolving Credit Agreement | Minimum | Commercial Paper | Base Rate
Debt Instrument [Line Items]
Basis spread percent													0.00%
Five Year Unsecured Revolving Credit Agreement | Minimum | Commercial Paper | Secured Overnight Financing Rate (SOFR) Rate
Debt Instrument [Line Items]
Basis spread percent													75.00%
Five Year Unsecured Revolving Credit Agreement | Maximum | Commercial Paper | Base Rate
Debt Instrument [Line Items]
Basis spread percent													25.00%
Five Year Unsecured Revolving Credit Agreement | Maximum | Commercial Paper | Secured Overnight Financing Rate (SOFR) Rate
Debt Instrument [Line Items]
Basis spread percent													125.00%
Five Year Unsecured Revolving Credit Agreement | Weighted Average | Commercial Paper
Debt Instrument [Line Items]
Debt term													1 month
$900 Million Revolving Credit Facility | Revolving Credit Facility
Debt Instrument [Line Items]
Maximum borrowing capacity									$ 900,000,000				$ 900,000,000
Debt term													3 years
Credit facility, accordion feature									100,000,000				$ 100,000,000
Loan increase potential									1,000,000,000				1,000,000,000
Line of credit borrowings outstanding									0	0			$ 0	0
$900 Million Revolving Credit Facility | Minimum | Revolving Credit Facility | Base Rate
Debt Instrument [Line Items]
Basis spread percent													0.00%
$900 Million Revolving Credit Facility | Minimum | Revolving Credit Facility | Secured Overnight Financing Rate (SOFR) Rate
Debt Instrument [Line Items]
Basis spread percent													75.00%
$900 Million Revolving Credit Facility | Maximum | Revolving Credit Facility | Base Rate
Debt Instrument [Line Items]
Basis spread percent													25.00%
$900 Million Revolving Credit Facility | Maximum | Revolving Credit Facility | Secured Overnight Financing Rate (SOFR) Rate
Debt Instrument [Line Items]
Basis spread percent													125.00%
$50 Million Revolving Credit Facility | 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