Income Taxes (Summary Of Tax Credit Carryforwards) (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2015
Carryforwards [Line Items]
Net operating losses, deferred tax assets	$ 560
IPL [Member]
Carryforwards [Line Items]
Net operating losses, deferred tax assets	230
WPL [Member]
Carryforwards [Line Items]
Net operating losses, deferred tax assets	210
Federal [Member]
Carryforwards [Line Items]
Net operating losses, carryforward amount	894
Net operating losses, deferred tax assets	306
Tax credits, carryforward amount	214
Tax credits, deferred tax assets	210
Federal [Member] \| IPL [Member]
Carryforwards [Line Items]
Net operating losses, carryforward amount	424
Net operating losses, deferred tax assets	145
Tax credits, carryforward amount	73
Tax credits, deferred tax assets	72
Federal [Member] \| WPL [Member]
Carryforwards [Line Items]
Net operating losses, carryforward amount	355
Net operating losses, deferred tax assets	122
Tax credits, carryforward amount	82
Tax credits, deferred tax assets	80
State [Member]
Carryforwards [Line Items]
Net operating losses, carryforward amount	853
Net operating losses, deferred tax assets	44
State [Member] \| IPL [Member]
Carryforwards [Line Items]
Net operating losses, carryforward amount	260
Net operating losses, deferred tax assets	13
State [Member] \| WPL [Member]
Carryforwards [Line Items]
Net operating losses, carryforward amount	166
Net operating losses, deferred tax assets	$ 8

Amount before allocation of valuation allowances of deferred tax asset attributable to deductible operating loss carryforwards.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 740

-SubTopic 10

-Section 50

-Paragraph 6

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Reference 3: http://www.xbrl.org/2003/role/presentationRef

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-Name Accounting Standards Codification

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Amount of operating loss carryforward, before tax effects, available to reduce future taxable income under enacted tax laws.

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The amount of the tax credit carryforward, before tax effects, available to reduce future taxable income under enacted tax laws.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

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Reference 2: http://www.xbrl.org/2003/role/presentationRef

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Amount of deferred tax asset, before valuation allowance, attributable to deductible other tax carryforwards.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef

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