Derivative Instruments and Hedging Activities - Schedule of Notional Amounts (Details) € in Millions, kWh in Millions, gal in Millions, DTH in Millions, $ in Millions	Sep. 30, 2021 USD ($) gal DTH kWh	Sep. 30, 2021 EUR (€) gal DTH kWh	Sep. 30, 2020 USD ($) DTH gal kWh	Sep. 30, 2020 EUR (€) DTH gal kWh
Commodity contracts | Propane
Derivative [Line Items]
Notional amount (in units) | gal	708	708	846	846
Commodity contracts | Electricity
Derivative [Line Items]
Notional amount (in units) | kWh	4,302	4,302	4,705	4,705
Natural gas futures, forward, basis swap, options and pipeline contracts | Natural Gas
Derivative [Line Items]
Notional amount (in units)	355	355	339	339
Interest rate swaps
Derivative [Line Items]
Notional amount	$ 1,421	€ 300	$ 1,344	€ 300
Forward foreign exchange contracts
Derivative [Line Items]
Notional amount	$ 509	€ 173	$ 511	€ 173
Regulated Utility Operations | Commodity contracts | Natural Gas
Derivative [Line Items]
Notional amount (in units)	20	20	22	22