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Benefit Plans (Narrative) (Details) $ / shares in Units, $ in Millions | 3 Months Ended
--- | ---
Mar. 31, 2019 USD ($) $ / shares shares
Defined Benefit Plan Disclosure [Line Items] |
Unrecognized compensation cost | $ | $ 13.7
Minimum [Member] |
Defined Benefit Plan Disclosure [Line Items] |
Unrecognized compensation cost recognized over a weighted average period | 1 year
Maximum [Member] |
Defined Benefit Plan Disclosure [Line Items] |
Unrecognized compensation cost recognized over a weighted average period | 2 years
IPL [Member] |
Defined Benefit Plan Disclosure [Line Items] |
Unrecognized compensation cost | $ | $ 7.6
WPL [Member] |
Defined Benefit Plan Disclosure [Line Items] |
Unrecognized compensation cost | $ | $ 5.6
Performance Shares [Member] |
Defined Benefit Plan Disclosure [Line Items] |
Performance period | 3 years
Granted (in shares/awards) | 80,837
Granted, weighted average grant date fair value (in dollars per share) | $ / shares | $ 46.35
Actual number of shares paid out upon vesting, minimum percentage of target shares | 0.00%
Actual number of shares paid out upon vesting, maximum percentage of target shares | 200.00%
Performance Restricted Stock Unit [Member] |
Defined Benefit Plan Disclosure [Line Items] |
Performance period | 3 years
Granted (in shares/awards) | 80,837
Granted, weighted average grant date fair value (in dollars per share) | $ / shares | $ 45.63
Actual number of shares paid out upon vesting, minimum percentage of target shares | 0.00%
Actual number of shares paid out upon vesting, maximum percentage of target shares | 200.00%
Instrument valuation based on shares of common stock, number of shares | 1
Restricted Stock Units (RSUs) [Member] |
Defined Benefit Plan Disclosure [Line Items] |
Performance period | 3 years
Granted (in shares/awards) | 95,938
Granted, weighted average grant date fair value (in dollars per share) | $ / shares | $ 45.63
Instrument valuation based on shares of common stock, number of shares | 1

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- Definition Unrecognized cost of unvested share-based compensation awards. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (i) -URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901 + Details
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- Definition Weighted average period over which unrecognized compensation is expected to be recognized for equity-based compensation plans, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (i) -URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901 + Details
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- Definition The weighted average fair value at grant date for nonvested equity-based awards issued during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan). + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(2)(iii)(1) -URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901 + Details
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