Income Taxes (Summary Of Tax Credit Carryforwards) (Details) $ in Millions	Sep. 30, 2017 USD ($)
Federal [Member]
Carryforwards [Line Items]
Net operating losses, carryforward amount	$ 815
Tax credits, carryforward amount	297
Federal [Member] | IPL [Member]
Carryforwards [Line Items]
Net operating losses, carryforward amount	500
Tax credits, carryforward amount	110
Federal [Member] | WPL [Member]
Carryforwards [Line Items]
Net operating losses, carryforward amount	208
Tax credits, carryforward amount	125
State [Member]
Carryforwards [Line Items]
Net operating losses, carryforward amount	701
State [Member] | IPL [Member]
Carryforwards [Line Items]
Net operating losses, carryforward amount	14
State [Member] | WPL [Member]
Carryforwards [Line Items]
Net operating losses, carryforward amount	$ 2