Income Taxes (Summary Of Tax Credit Carryforwards) (Details) $ in Millions	Jun. 30, 2015 USD ($)
Carryforwards [Line Items]
Net operating losses, deferred tax assets	$ 552
IPL [Member]
Carryforwards [Line Items]
Net operating losses, deferred tax assets	225
WPL [Member]
Carryforwards [Line Items]
Net operating losses, deferred tax assets	210
Federal [Member]
Carryforwards [Line Items]
Net operating losses, carryforward amount	845
Net operating losses, deferred tax assets	290
Tax credits, carryforward amount	222
Tax credits, deferred tax assets	218
Federal [Member] | IPL [Member]
Carryforwards [Line Items]
Net operating losses, carryforward amount	396
Net operating losses, deferred tax assets	136
Tax credits, carryforward amount	77
Tax credits, deferred tax assets	75
Federal [Member] | WPL [Member]
Carryforwards [Line Items]
Net operating losses, carryforward amount	342
Net operating losses, deferred tax assets	117
Tax credits, carryforward amount	86
Tax credits, deferred tax assets	85
State [Member]
Carryforwards [Line Items]
Net operating losses, carryforward amount	860
Net operating losses, deferred tax assets	44
State [Member] | IPL [Member]
Carryforwards [Line Items]
Net operating losses, carryforward amount	265
Net operating losses, deferred tax assets	14
State [Member] | WPL [Member]
Carryforwards [Line Items]
Net operating losses, carryforward amount	170
Net operating losses, deferred tax assets	$ 8