Income Taxes (Summary Of Tax Credit Carryforwards) (Details) $ in Millions	Dec. 31, 2016 USD ($)
Federal [Member]
Tax carryforwards, net operating losses	$ 506
Tax carryforwards, tax credits	274
Federal [Member] | IPL [Member]
Tax carryforwards, net operating losses	206
Tax carryforwards, tax credits	100
Federal [Member] | WPL [Member]
Tax carryforwards, net operating losses	215
Tax carryforwards, tax credits	113
State [Member]
Tax carryforwards, net operating losses	673
State [Member] | IPL [Member]
Tax carryforwards, net operating losses	12
State [Member] | WPL [Member]
Tax carryforwards, net operating losses	$ 2