Derivative Instruments and Hedging Activities - Schedule of Notional Amounts (Details) € in Millions, kWh in Millions, gal in Millions, DTH in Millions, $ in Millions	Mar. 31, 2023 USD ($) gal kWh DTH	Mar. 31, 2023 EUR (€) gal kWh DTH	Sep. 30, 2022 USD ($) DTH gal kWh	Sep. 30, 2022 EUR (€) DTH gal kWh	Mar. 31, 2022 USD ($) kWh DTH gal	Mar. 31, 2022 EUR (€) kWh DTH gal
Commodity contracts | Regulated Utility Operations | Natural Gas
Derivative [Line Items]
Notional amount (in units)	12	12	19	19	11	11
Commodity contracts | Non-utility Operations | LPG swaps
Derivative [Line Items]
Notional amount (in units) | gal	691	691	874	874	622	622
Commodity contracts | Non-utility Operations | Electricity forward and futures contracts
Derivative [Line Items]
Notional amount (in units) | kWh	1,890	1,890	2,446	2,446	3,098	3,098
Natural gas futures, forward and pipeline contracts (in dekatherms) | Non-utility Operations | Natural Gas
Derivative [Line Items]
Notional amount (in units)	366	366	363	363	346	346
Interest rate swaps
Derivative [Line Items]
Notional amount	$ 1,277	€ 300	$ 1,358	€ 300	$ 1,414	€ 300
Forward foreign currency exchange contracts
Derivative [Line Items]
Notional amount	$ 285	€ 331	$ 465	€ 411	$ 274	€ 486