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Benefit Plans (Narrative) (Details) $ / shares in Units, $ in Millions | 9 Months Ended
--- | ---
Sep. 30, 2019 USD ($) $ / shares shares
Defined Benefit Plan Disclosure [Line Items] |
Unrecognized compensation cost | $ | $ 7.2
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 | $ | $ 4.0
WPL [Member] |
Defined Benefit Plan Disclosure [Line Items] |
Unrecognized compensation cost | $ | $ 2.9
Performance Shares [Member] |
Defined Benefit Plan Disclosure [Line Items] |
Performance period | 3 years
Granted (in shares/awards) | 91,816
Granted, weighted average grant date fair value (in dollars per share) | $ / shares | $ 47.23
Shares included in diluted earnings per share (in shares) | 122,720
Performance Shares [Member] | Minimum [Member] |
Defined Benefit Plan Disclosure [Line Items] |
Actual number of shares paid out upon vesting, percentage of target shares | 0.00%
Performance Shares [Member] | Maximum [Member] |
Defined Benefit Plan Disclosure [Line Items] |
Actual number of shares paid out upon vesting, 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) | 91,816
Granted, weighted average grant date fair value (in dollars per share) | $ / shares | $ 46.10
Instrument valuation based on shares of common stock, number of shares | 1
Performance Restricted Stock Unit [Member] | Minimum [Member] |
Defined Benefit Plan Disclosure [Line Items] |
Actual number of shares paid out upon vesting, percentage of target shares | 0.00%
Performance Restricted Stock Unit [Member] | Maximum [Member] |
Defined Benefit Plan Disclosure [Line Items] |
Actual number of shares paid out upon vesting, percentage of target shares | 200.00%
Restricted Stock Units [Member] |
Defined Benefit Plan Disclosure [Line Items] |
Performance period | 3 years
Granted (in shares/awards) | 105,348
Granted, weighted average grant date fair value (in dollars per share) | $ / shares | $ 45.98
Instrument valuation based on shares of common stock, number of shares | 1

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