Derivative Instruments and Hedging Activities - Schedule of Notional Amounts (Details) € in Millions, kWh in Millions, gal in Millions, DTH in Millions, $ in Millions	Jun. 30, 2021 USD ($) kWh DTH gal	Jun. 30, 2021 EUR (€) kWh DTH gal	Sep. 30, 2020 USD ($) DTH kWh gal	Sep. 30, 2020 EUR (€) DTH kWh gal	Jun. 30, 2020 USD ($) DTH kWh gal	Jun. 30, 2020 EUR (€) DTH kWh gal
Interest rate swaps
Derivative [Line Items]
Notional amount	$ 1,424	€ 300	$ 1,344	€ 300	$ 1,347	€ 300
Forward foreign currency exchange contracts
Derivative [Line Items]
Notional amount	$ 504	€ 173	$ 511	€ 173	$ 440	€ 173
Regulated Utility Operations | Commodity contracts | Natural Gas
Derivative [Line Items]
Notional amount (in units)	12	12	22	22	16	16
Non-utility Operations | Commodity contracts | LPG
Derivative [Line Items]
Notional amount (in units) | gal	688	688	846	846	890	890
Non-utility Operations | Commodity contracts | Electricity | Long
Derivative [Line Items]
Notional amount (in units) | kWh	4,730	4,730	4,705	4,705	4,144	4,144
Non-utility Operations | Natural gas futures, forward and pipeline contracts (in dekatherms) | Natural Gas
Derivative [Line Items]
Notional amount (in units)	344	344	339	339	343	343