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, 2022 USD ($) DTH gal kWh	Mar. 31, 2022 EUR (€) DTH gal kWh	Sep. 30, 2021 USD ($) kWh DTH gal	Sep. 30, 2021 EUR (€) kWh DTH gal	Mar. 31, 2021 USD ($) kWh gal DTH	Mar. 31, 2021 EUR (€) kWh gal DTH
Commodity contracts | Regulated Utility Operations | Natural Gas
Derivative [Line Items]
Notional amount (in units)	11	11	20	20	12	12
Commodity contracts | Non-utility Operations | LPG
Derivative [Line Items]
Notional amount (in units) | gal	622	622	708	708	557	557
Commodity contracts | Non-utility Operations | Electricity
Derivative [Line Items]
Notional amount (in units) | kWh	3,098	3,098	4,302	4,302	4,773	4,773
Natural gas futures, forward and pipeline contracts (in dekatherms) | Non-utility Operations | Natural Gas
Derivative [Line Items]
Notional amount (in units)	346	346	355	355	338	338
Interest rate swaps
Derivative [Line Items]
Notional amount	$ 1,414	€ 300	$ 1,421	€ 300	$ 1,302	€ 300
Forward foreign currency exchange contracts
Derivative [Line Items]
Notional amount	$ 274	€ 486	$ 509	€ 173	$ 384	€ 173