Income Taxes (Summary Of Tax Credit Carryforwards) (Details) $ in Millions	Jun. 30, 2016 USD ($)
Carryforwards [Line Items]
Net operating losses, deferred tax assets	$ 557
IPL [Member]
Carryforwards [Line Items]
Net operating losses, deferred tax assets	208
WPL [Member]
Carryforwards [Line Items]
Net operating losses, deferred tax assets	216
Federal [Member]
Carryforwards [Line Items]
Net operating losses, carryforward amount	769
Net operating losses, deferred tax assets	264
Tax credits, carryforward amount	258
Tax credits, deferred tax assets	254
Federal [Member] \| IPL [Member]
Carryforwards [Line Items]
Net operating losses, carryforward amount	349
Net operating losses, deferred tax assets	117
Tax credits, carryforward amount	93
Tax credits, deferred tax assets	90
Federal [Member] \| WPL [Member]
Carryforwards [Line Items]
Net operating losses, carryforward amount	311
Net operating losses, deferred tax assets	109
Tax credits, carryforward amount	105
Tax credits, deferred tax assets	105
State [Member]
Carryforwards [Line Items]
Net operating losses, carryforward amount	747
Net operating losses, deferred tax assets	39
State [Member] \| IPL [Member]
Carryforwards [Line Items]
Net operating losses, carryforward amount	20
Net operating losses, deferred tax assets	1
State [Member] \| WPL [Member]
Carryforwards [Line Items]
Net operating losses, carryforward amount	38
Net operating losses, deferred tax assets	$ 2

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 25
-Paragraph 20
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=68052875&loc=d3e28680-109314

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 6
-URI http://asc.fasb.org/extlink&oid=65882285&loc=d3e32621-109319

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=65882285&loc=d3e32632-109319

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Amount, before allocation of a valuation allowances, of deferred tax assets attributable to deductible tax credit carryforwards including, but not limited to, research, foreign, general business, alternative minimum tax, and other deductible tax credit carryforwards.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 6
-URI http://asc.fasb.org/extlink&oid=65882285&loc=d3e32621-109319

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 3
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=65882285&loc=d3e32559-109319

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Carryforwards
-URI http://asc.fasb.org/extlink&oid=6506874

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=65882285&loc=d3e32632-109319

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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
-Publisher FASB
-Name Accounting Standards Codification
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Reference 2: http://www.xbrl.org/2003/role/presentationRef
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-Name Accounting Standards Codification
-Glossary Carryforwards
-URI http://asc.fasb.org/extlink&oid=6506874

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