Income Taxes (Summary Of Tax Credit Carryforwards) (Details) $ in Millions	Sep. 30, 2019 USD ($)
Federal [Member]
Carryforwards [Line Items]
Net operating losses, carryforward amount	$ 611
Tax credits, carryforward amount	337
Federal [Member] | IPL [Member]
Carryforwards [Line Items]
Net operating losses, carryforward amount	522
Tax credits, carryforward amount	162
Federal [Member] | WPL [Member]
Carryforwards [Line Items]
Net operating losses, carryforward amount	41
Tax credits, carryforward amount	156
State [Member]
Carryforwards [Line Items]
Net operating losses, carryforward amount	677
State [Member] | IPL [Member]
Carryforwards [Line Items]
Net operating losses, carryforward amount	12
State [Member] | WPL [Member]
Carryforwards [Line Items]
Net operating losses, carryforward amount	$ 2