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Related Parties (Service Agreements) (Details) - Corporate Services [Member] - Subsidiary of Common Parent [Member] - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Administrative and General Services Billings [Member] | IPL [Member] |  |  |
Related Party Transaction [Line Items] |  |  |
Amounts billed between related parties | $ 177 | $ 161 | $ 150
Administrative and General Services Billings [Member] | WPL [Member] |  |  |
Related Party Transaction [Line Items] |  |  |
Amounts billed between related parties | 135 | 133 | 121
Transmission Sales Credited [Member] | IPL [Member] |  |  |
Related Party Transaction [Line Items] |  |  |
Amounts billed between related parties | 23 | 8 | 10
Transmission Sales Credited [Member] | WPL [Member] |  |  |
Related Party Transaction [Line Items] |  |  |
Amounts billed between related parties | 13 | 7 | 24
Transmission Purchases Billed [Member] | IPL [Member] |  |  |
Related Party Transaction [Line Items] |  |  |
Amounts billed between related parties | 364 | 433 | 366
Transmission Purchases Billed [Member] | WPL [Member] |  |  |
Related Party Transaction [Line Items] |  |  |
Amounts billed between related parties | $ 115 | $ 102 | $ 66

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- Definition Amount of transactions with related party during the financial reporting period. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 850 -SubTopic 10 -Section 50 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=6457730&loc=d3e39603-107864 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 850 -SubTopic 10 -Section 50 -Paragraph 1 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=6457730&loc=d3e39549-107864 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 850 -SubTopic 10 -Section 50 -Paragraph 4 -URI http://asc.fasb.org/extlink&oid=6457730&loc=d3e39622-107864 + Details
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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
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- Details
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- Details
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- Details
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- Details
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- Details
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- Details
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- Details
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