Income Taxes (Summary Of Tax Credit Carryforwards) (Details) $ in Millions	Dec. 31, 2020 USD ($)
Federal [Member]
Tax carryforwards, net operating losses	$ 366
Tax carryforwards, tax credits	454
Federal [Member] | IPL [Member]
Tax carryforwards, net operating losses	339
Tax carryforwards, tax credits	258
Federal [Member] | WPL [Member]
Tax carryforwards, net operating losses	3
Tax carryforwards, tax credits	175
State [Member]
Tax carryforwards, net operating losses	622
State [Member] | IPL [Member]
Tax carryforwards, net operating losses	10
State [Member] | WPL [Member]
Tax carryforwards, net operating losses	$ 2