Income Taxes (Summary Of Tax Credit Carryforwards) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012
Operating Loss Carryforwards [Line Items]
Deferred tax assets, net operating losses	$ 487
IPL [Member]
Operating Loss Carryforwards [Line Items]
Deferred tax assets, net operating losses	183
WPL [Member]
Operating Loss Carryforwards [Line Items]
Deferred tax assets, net operating losses	189
Federal [Member]
Operating Loss Carryforwards [Line Items]
Tax carryforwards, net operating losses	892
Deferred tax assets, net operating losses	306
Earliest expiration date, net operating losses	2029
Tax carryforwards, tax credits	136
Deferred tax assets, tax credits	134
Earliest expiration date, tax credits	2022
Federal [Member] | IPL [Member]
Operating Loss Carryforwards [Line Items]
Tax carryforwards, net operating losses	382
Deferred tax assets, net operating losses	131
Earliest expiration date, net operating losses	2029
Tax carryforwards, tax credits	38
Deferred tax assets, tax credits	37
Earliest expiration date, tax credits	2022
Federal [Member] | WPL [Member]
Operating Loss Carryforwards [Line Items]
Tax carryforwards, net operating losses	414
Deferred tax assets, net operating losses	142
Earliest expiration date, net operating losses	2029
Tax carryforwards, tax credits	40
Deferred tax assets, tax credits	39
Earliest expiration date, tax credits	2022
State [Member]
Operating Loss Carryforwards [Line Items]
Tax carryforwards, net operating losses	871
Deferred tax assets, net operating losses	47
Earliest expiration date, net operating losses	2014
State [Member] | IPL [Member]
Operating Loss Carryforwards [Line Items]
Tax carryforwards, net operating losses	254
Deferred tax assets, net operating losses	15
Earliest expiration date, net operating losses	2018
State [Member] | WPL [Member]
Operating Loss Carryforwards [Line Items]
Tax carryforwards, net operating losses	152
Deferred tax assets, net operating losses	$ 8
Earliest expiration date, net operating losses	2018