Income Taxes (Summary Of Tax Credit Carryforwards) (Details) $ in Millions	Sep. 30, 2018 USD ($)
Federal [Member]
Carryforwards [Line Items]
Net operating losses, carryforward amount	$ 804
Tax credits, carryforward amount	290
Federal [Member] | IPL [Member]
Carryforwards [Line Items]
Net operating losses, carryforward amount	563
Tax credits, carryforward amount	129
Federal [Member] | WPL [Member]
Carryforwards [Line Items]
Net operating losses, carryforward amount	144
Tax credits, carryforward amount	143
State [Member]
Carryforwards [Line Items]
Net operating losses, carryforward amount	765
State [Member] | IPL [Member]
Carryforwards [Line Items]
Net operating losses, carryforward amount	13
State [Member] | WPL [Member]
Carryforwards [Line Items]
Net operating losses, carryforward amount	$ 2