Income Taxes (Summary Of Tax Credit Carryforwards) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2013
Operating Loss Carryforwards [Line Items]
Deferred tax assets, net operating losses	$ 455
IPL [Member]
Operating Loss Carryforwards [Line Items]
Deferred tax assets, net operating losses	174
WPL [Member]
Operating Loss Carryforwards [Line Items]
Deferred tax assets, net operating losses	169
Federal [Member]
Operating Loss Carryforwards [Line Items]
Tax carryforwards, net operating losses	735
Deferred tax assets, net operating losses	252
Tax carryforwards, tax credits	170
Deferred tax assets, tax credits	168
Federal [Member] | IPL [Member]
Operating Loss Carryforwards [Line Items]
Tax carryforwards, net operating losses	325
Deferred tax assets, net operating losses	111
Tax carryforwards, tax credits	54
Deferred tax assets, tax credits	53
Federal [Member] | WPL [Member]
Operating Loss Carryforwards [Line Items]
Tax carryforwards, net operating losses	312
Deferred tax assets, net operating losses	107
Tax carryforwards, tax credits	58
Deferred tax assets, tax credits	57
State [Member]
Operating Loss Carryforwards [Line Items]
Tax carryforwards, net operating losses	686
Deferred tax assets, net operating losses	35
State [Member] | IPL [Member]
Operating Loss Carryforwards [Line Items]
Tax carryforwards, net operating losses	189
Deferred tax assets, net operating losses	10
State [Member] | WPL [Member]
Operating Loss Carryforwards [Line Items]
Tax carryforwards, net operating losses	99
Deferred tax assets, net operating losses	$ 5