Income Taxes (Summary Of Tax Credit Carryforwards) (Details) $ in Millions	Sep. 30, 2021 USD ($)
Federal [Member]
Carryforwards [Line Items]
Net operating losses, carryforward amount	$ 170
Tax credits, carryforward amount	547
Federal [Member] | IPL [Member]
Carryforwards [Line Items]
Net operating losses, carryforward amount	157
Tax credits, carryforward amount	339
Federal [Member] | WPL [Member]
Carryforwards [Line Items]
Net operating losses, carryforward amount	1
Tax credits, carryforward amount	186
State [Member]
Carryforwards [Line Items]
Net operating losses, carryforward amount	592
State [Member] | IPL [Member]
Carryforwards [Line Items]
Net operating losses, carryforward amount	24
State [Member] | WPL [Member]
Carryforwards [Line Items]
Net operating losses, carryforward amount	$ 2