Income Taxes (Summary Of Tax Credit Carryforwards) (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2013
Operating Loss Carryforwards [Line Items]
Net operating losses, deferred tax assets	$ 464
IPL [Member]
Operating Loss Carryforwards [Line Items]
Net operating losses, deferred tax assets	176
WPL [Member]
Operating Loss Carryforwards [Line Items]
Net operating losses, deferred tax assets	172
Federal [Member]
Operating Loss Carryforwards [Line Items]
Net operating losses, carryforward amount	775
Net operating losses, deferred tax assets	266
Tax credits, carryforward amount	161
Tax credits, deferred tax asset	159
Federal [Member] | IPL [Member]
Operating Loss Carryforwards [Line Items]
Net operating losses, carryforward amount	344
Net operating losses, deferred tax assets	118
Tax credits, carryforward amount	49
Tax credits, deferred tax asset	48
Federal [Member] | WPL [Member]
Operating Loss Carryforwards [Line Items]
Net operating losses, carryforward amount	321
Net operating losses, deferred tax assets	110
Tax credits, carryforward amount	54
Tax credits, deferred tax asset	53
State [Member]
Operating Loss Carryforwards [Line Items]
Net operating losses, carryforward amount	753
Net operating losses, deferred tax assets	39
State [Member] | IPL [Member]
Operating Loss Carryforwards [Line Items]
Net operating losses, carryforward amount	189
Net operating losses, deferred tax assets	10
State [Member] | WPL [Member]
Operating Loss Carryforwards [Line Items]
Net operating losses, carryforward amount	177
Net operating losses, deferred tax assets	$ 9