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Common Equity (Narrative) (Details) - USD ($) $ in Millions | 3 Months Ended | 9 Months Ended
--- | --- | ---
Sep. 30, 2017 | Sep. 30, 2016 | Sep. 30, 2017 | Sep. 30, 2016
Common Equity [Line Items] |  |  |  |
Proceeds from issuance of common stock, net |  |  | $ 143.2 | $ 20.4
Comprehensive income | $ 0.0 | $ 0.0 | 0.0 | 0.0
IPL [Member] |  |  |  |
Common Equity [Line Items] |  |  |  |
Retained earnings free of dividend restrictions | 701.0 |  | 701.0 |
Restricted net assets of subsidiaries | 1,700.0 |  | 1,700.0 |
Comprehensive income | 0.0 | 0.0 | 0.0 | 0.0
WPL [Member] |  |  |  |
Common Equity [Line Items] |  |  |  |
Retained earnings free of dividend restrictions | 32.0 |  | 32.0 |
Restricted net assets of subsidiaries | 1,800.0 |  | 1,800.0 |
Comprehensive income | $ 0.0 | $ 0.0 | 0.0 | $ 0.0
At-The-Market Offering Program [Member] |  |  |  |
Common Equity [Line Items] |  |  |  |
Maximum aggregate gross sales price of common stock that can be offered and sold |  |  | $ 125.0 |
At-the-market offering program issuances (in shares) |  |  | 3,074,931 |
Proceeds from issuance of common stock, net |  |  | $ 124.0 |
Commissions and fees from issuance of common stock |  |  | $ 1.0 |

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- Definition Amount of restricted net assets of consolidated and unconsolidated subsidiaries as of the end of the most recently completed fiscal year. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 235 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.4-08.(e)(3)(ii)) -URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690 + Details
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