Income Taxes (Summary Of Tax Credit Carryforwards) (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2014
Operating Loss Carryforwards [Line Items]
Net operating losses, deferred tax assets	$ 451
IPL [Member]
Operating Loss Carryforwards [Line Items]
Net operating losses, deferred tax assets	170
WPL [Member]
Operating Loss Carryforwards [Line Items]
Net operating losses, deferred tax assets	170
Federal [Member]
Operating Loss Carryforwards [Line Items]
Net operating losses, carryforward amount	697
Net operating losses, deferred tax assets	239
Tax credits, carryforward amount	181
Tax credits, deferred tax assets	178
Federal [Member] | IPL [Member]
Operating Loss Carryforwards [Line Items]
Net operating losses, carryforward amount	303
Net operating losses, deferred tax assets	104
Tax credits, carryforward amount	59
Tax credits, deferred tax assets	58
Federal [Member] | WPL [Member]
Operating Loss Carryforwards [Line Items]
Net operating losses, carryforward amount	302
Net operating losses, deferred tax assets	103
Tax credits, carryforward amount	64
Tax credits, deferred tax assets	62
State [Member]
Operating Loss Carryforwards [Line Items]
Net operating losses, carryforward amount	681
Net operating losses, deferred tax assets	34
State [Member] | IPL [Member]
Operating Loss Carryforwards [Line Items]
Net operating losses, carryforward amount	172
Net operating losses, deferred tax assets	8
State [Member] | WPL [Member]
Operating Loss Carryforwards [Line Items]
Net operating losses, carryforward amount	96
Net operating losses, deferred tax assets	$ 5