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