Income Taxes (Summary Of Tax Credit Carryforwards) (Details) $ in Millions	Mar. 31, 2019 USD ($)
Federal [Member]
Carryforwards [Line Items]
Net operating losses, carryforward amount	$ 776
Tax credits, carryforward amount	307
Federal [Member] | IPL [Member]
Carryforwards [Line Items]
Net operating losses, carryforward amount	551
Tax credits, carryforward amount	138
Federal [Member] | WPL [Member]
Carryforwards [Line Items]
Net operating losses, carryforward amount	129
Tax credits, carryforward amount	151
State [Member]
Carryforwards [Line Items]
Net operating losses, carryforward amount	785
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	$ 2