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Income Taxes (Summary Of Tax Credit Carryforwards) (Details) $ in Millions | Mar. 31, 2016 USD ($)
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Carryforwards [Line Items] |
Net operating losses, deferred tax assets | $ 537
IPL [Member] |
Carryforwards [Line Items] |
Net operating losses, deferred tax assets | 198
WPL [Member] |
Carryforwards [Line Items] |
Net operating losses, deferred tax assets | 207
Federal [Member] |
Carryforwards [Line Items] |
Net operating losses, carryforward amount | 733
Net operating losses, deferred tax assets | 252
Tax credits, carryforward amount | 250
Tax credits, deferred tax assets | 246
Federal [Member] | IPL [Member] |
Carryforwards [Line Items] |
Net operating losses, carryforward amount | 330
Net operating losses, deferred tax assets | 111
Tax credits, carryforward amount | 89
Tax credits, deferred tax assets | 86
Federal [Member] | WPL [Member] |
Carryforwards [Line Items] |
Net operating losses, carryforward amount | 298
Net operating losses, deferred tax assets | 104
Tax credits, carryforward amount | 101
Tax credits, deferred tax assets | 101
State [Member] |
Carryforwards [Line Items] |
Net operating losses, carryforward amount | 748
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 | 47
Net operating losses, deferred tax assets | $ 2

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- Definition Amount before allocation of valuation allowances of deferred tax asset attributable to deductible operating loss carryforwards. + References 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=29652012&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=6907707&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=6907707&loc=d3e32632-109319 + Details
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- Definition Amount of operating loss 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 -Topic 740 -SubTopic 10 -Section 50 -Paragraph 3 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=6907707&loc=d3e32559-109319 + Details
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- Definition 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 -Topic 740 -SubTopic 10 -Section 50 -Paragraph 3 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=6907707&loc=d3e32559-109319 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Carryforwards -URI http://asc.fasb.org/extlink&oid=6506874 + Details
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- Definition Amount of deferred tax asset, before valuation allowance, attributable to deductible other tax carryforwards. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=6907707&loc=d3e32537-109319 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 30 -Paragraph 5 -Subparagraph (d) -URI http://asc.fasb.org/extlink&oid=6907311&loc=d3e30536-109315 + Details
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