Income Taxes (Summary Of Tax Credit Carryforwards) (Details) $ in Millions	Jun. 30, 2018 USD ($)
Federal [Member]
Carryforwards [Line Items]
Net operating losses, carryforward amount	$ 759
Tax credits, carryforward amount	284
Federal [Member] | IPL [Member]
Carryforwards [Line Items]
Net operating losses, carryforward amount	490
Tax credits, carryforward amount	127
Federal [Member] | WPL [Member]
Carryforwards [Line Items]
Net operating losses, carryforward amount	170
Tax credits, carryforward amount	140
State [Member]
Carryforwards [Line Items]
Net operating losses, carryforward amount	732
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	$ 22