Income Taxes (Summary Of Tax Credit Carryforwards) (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2014
Carryforwards [Line Items]
Net operating losses, deferred tax assets	$ 471
IPL [Member]
Carryforwards [Line Items]
Net operating losses, deferred tax assets	180
WPL [Member]
Carryforwards [Line Items]
Net operating losses, deferred tax assets	180
Federal [Member]
Carryforwards [Line Items]
Net operating losses, carryforward amount	710
Net operating losses, deferred tax assets	244
Tax credits, carryforward amount	193
Tax credits, deferred tax assets	190
Federal [Member] | IPL [Member]
Carryforwards [Line Items]
Net operating losses, carryforward amount	310
Net operating losses, deferred tax assets	106
Tax credits, carryforward amount	64
Tax credits, deferred tax assets	63
Federal [Member] | WPL [Member]
Carryforwards [Line Items]
Net operating losses, carryforward amount	305
Net operating losses, deferred tax assets	105
Tax credits, carryforward amount	71
Tax credits, deferred tax assets	69
State [Member]
Carryforwards [Line Items]
Net operating losses, carryforward amount	744
Net operating losses, deferred tax assets	37
State [Member] | IPL [Member]
Carryforwards [Line Items]
Net operating losses, carryforward amount	217
Net operating losses, deferred tax assets	11
State [Member] | WPL [Member]
Carryforwards [Line Items]
Net operating losses, carryforward amount	116
Net operating losses, deferred tax assets	$ 6