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Benefit Plans (Narrative) (Details)
$ / shares in Units, $ in Millions
6 Months Ended
Jun. 30, 2019
USD ($)
$ / shares
shares
Defined Benefit Plan Disclosure [Line Items]  
Unrecognized compensation cost | $ $ 10.3
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 | $ $ 5.7
WPL [Member]  
Defined Benefit Plan Disclosure [Line Items]  
Unrecognized compensation cost | $ $ 4.2
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
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) 80,837
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
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) 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