Income Taxes (Summary Of Tax Credit Carryforwards) (Details) $ in Millions	Dec. 31, 2018 USD ($)
Federal [Member]
Tax carryforwards, net operating losses	$ 766
Tax carryforwards, tax credits	299
Federal [Member] | IPL [Member]
Tax carryforwards, net operating losses	551
Tax carryforwards, tax credits	133
Federal [Member] | WPL [Member]
Tax carryforwards, net operating losses	126
Tax carryforwards, tax credits	147
State [Member]
Tax carryforwards, net operating losses	792
State [Member] | IPL [Member]
Tax carryforwards, net operating losses	13
State [Member] | WPL [Member]
Tax carryforwards, net operating losses	$ 8