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Related Parties (Service Agreements) (Details) - Corporate Services [Member] - Subsidiary of Common Parent [Member] - USD ($) $ in Millions | 3 Months Ended | 9 Months Ended
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Sep. 30, 2017 | Sep. 30, 2016 | Sep. 30, 2017 | Sep. 30, 2016
Administrative and General Services Billings [Member] | IPL [Member] |  |  |  |
Related Party Transactions [Line Items] |  |  |  |
Amounts billed between related parties | $ 48 | $ 41 | $ 130 | $ 124
Administrative and General Services Billings [Member] | WPL [Member] |  |  |  |
Related Party Transactions [Line Items] |  |  |  |
Amounts billed between related parties | 37 | 33 | 100 | 103
Sales Credited [Member] | IPL [Member] |  |  |  |
Related Party Transactions [Line Items] |  |  |  |
Amounts billed between related parties | 8 | 4 | 15 | 7
Sales Credited [Member] | WPL [Member] |  |  |  |
Related Party Transactions [Line Items] |  |  |  |
Amounts billed between related parties | 6 | 3 | 8 | 6
Purchases Billed [Member] | IPL [Member] |  |  |  |
Related Party Transactions [Line Items] |  |  |  |
Amounts billed between related parties | 109 | 126 | 271 | 324
Purchases Billed [Member] | WPL [Member] |  |  |  |
Related Party Transactions [Line Items] |  |  |  |
Amounts billed between related parties | $ 32 | $ 23 | $ 99 | $ 65

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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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