Income Taxes (Summary Of Tax Credit Carryforwards) (Details) $ in Millions	Mar. 31, 2021 USD ($)
Federal [Member]
Carryforwards [Line Items]
Net operating losses, carryforward amount	$ 331
Tax credits, carryforward amount	481
Federal [Member] | IPL [Member]
Carryforwards [Line Items]
Net operating losses, carryforward amount	306
Tax credits, carryforward amount	280
Federal [Member] | WPL [Member]
Carryforwards [Line Items]
Net operating losses, carryforward amount	3
Tax credits, carryforward amount	180
State [Member]
Carryforwards [Line Items]
Net operating losses, carryforward amount	627
State [Member] | IPL [Member]
Carryforwards [Line Items]
Net operating losses, carryforward amount	16
State [Member] | WPL [Member]
Carryforwards [Line Items]
Net operating losses, carryforward amount	$ 2