Risk Management Activities and Derivative Transactions Counterparty Credit Risk (Details) $ in Millions |
3 Months Ended | 9 Months Ended | ||
---|---|---|---|---|
Jun. 30, 2020
USD ($)
megawatts
|
Jun. 30, 2020
USD ($)
megawatts
|
Jun. 30, 2019 |
Sep. 30, 2019
USD ($)
|
|
Derivative | ||||
Accounts Receivable, before Allowance for Credit Loss, Current | $ 1,286 | $ 1,286 | $ 1,624 | |
Total derivatives not subject to master netting or similar arrangement | $ 10 | $ 10 | $ 12 | |
Two Largest Customer Percentage of Total Operating Revenue | 1800.00% | 1700.00% | 1600.00% | |
Moody's, A1 Rating [Member] | ||||
Derivative | ||||
Banking Counterparties Credit Rating | A3 | |||
Natural Gas Banking Counterparties Credit Rating | A2 | |||
Moody's, B1 Rating [Member] | ||||
Derivative | ||||
Coal Banking Counterparties Credit Rating | B1 | |||
Moody's, Ba1 Rating [Member] | ||||
Derivative | ||||
Coal Banking Counterparties Credit Rating | Ba1 | |||
Moody's, Caa1 Rating [Member] | ||||
Derivative | ||||
Natural Gas Banking Counterparties Credit Rating | Caa2 | |||
Long-term Contract for Purchase of Electric Power [Domain] | ||||
Derivative | ||||
Megawatts | megawatts | 440 | 440 |