Income Taxes (Summary Of Tax Credit Carryforwards) (Details) (USD $) In Millions, unless otherwise specified	Jun. 30, 2014
Carryforwards [Line Items]
Net operating losses, deferred tax assets	$ 471
IPL [Member]
Carryforwards [Line Items]
Net operating losses, deferred tax assets	181
WPL [Member]
Carryforwards [Line Items]
Net operating losses, deferred tax assets	179
Federal [Member]
Carryforwards [Line Items]
Net operating losses, carryforward amount	721
Net operating losses, deferred tax assets	248
Tax credits, carryforward amount	188
Tax credits, deferred tax assets	185
Federal [Member] | IPL [Member]
Carryforwards [Line Items]
Net operating losses, carryforward amount	317
Net operating losses, deferred tax assets	109
Tax credits, carryforward amount	62
Tax credits, deferred tax assets	61
Federal [Member] | WPL [Member]
Carryforwards [Line Items]
Net operating losses, carryforward amount	308
Net operating losses, deferred tax assets	106
Tax credits, carryforward amount	68
Tax credits, deferred tax assets	67
State [Member]
Carryforwards [Line Items]
Net operating losses, carryforward amount	747
Net operating losses, deferred tax assets	38
State [Member] | IPL [Member]
Carryforwards [Line Items]
Net operating losses, carryforward amount	222
Net operating losses, deferred tax assets	11
State [Member] | WPL [Member]
Carryforwards [Line Items]
Net operating losses, carryforward amount	114
Net operating losses, deferred tax assets	$ 6