Income Taxes (Summary Of Tax Credit Carryforwards) (Details) $ in Millions	Mar. 31, 2020 USD ($)
Federal [Member]
Carryforwards [Line Items]
Net operating losses, carryforward amount	$ 280
Tax credits, carryforward amount	386
Federal [Member] | IPL [Member]
Carryforwards [Line Items]
Net operating losses, carryforward amount	260
Tax credits, carryforward amount	199
Federal [Member] | WPL [Member]
Carryforwards [Line Items]
Net operating losses, carryforward amount	2
Tax credits, carryforward amount	167
State [Member]
Carryforwards [Line Items]
Net operating losses, carryforward amount	606
State [Member] | IPL [Member]
Carryforwards [Line Items]
Net operating losses, carryforward amount	12
State [Member] | WPL [Member]
Carryforwards [Line Items]
Net operating losses, carryforward amount	$ 2