Benefit Plans (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
	Sep. 30, 2015	Sep. 30, 2016
Defined Benefit Plan Disclosure [Line Items]
Percentage of employees accepting voluntary separation package	2.00%
Voluntary employee separation charges	$ 8.0
Unrecognized compensation cost		$ 8.2
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]
Voluntary employee separation charges	5.0
WPL [Member]
Defined Benefit Plan Disclosure [Line Items]
Voluntary employee separation charges	$ 3.0
Performance Restricted Stock Unit And Performance Restricted Unit [Member]
Defined Benefit Plan Disclosure [Line Items]
Performance period		3 years
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 Units [Member]
Defined Benefit Plan Disclosure [Line Items]
Instrument valuation based on shares of common stock, number of shares		1
Performance Restricted Stock Unit [Member]
Defined Benefit Plan Disclosure [Line Items]
Instrument valuation based on shares of common stock, number of shares		1
Performance Restricted Unit [Member]
Defined Benefit Plan Disclosure [Line Items]
Instrument valuation based on shares of common stock, number of shares		1
Key Employee Performance Restricted Unit [Member]
Defined Benefit Plan Disclosure [Line Items]
Instrument valuation based on shares of common stock, number of shares		1
Restricted Stock Unit And Restricted Unit [Member]
Defined Benefit Plan Disclosure [Line Items]
Instrument valuation based on shares of common stock, number of shares		1
Performance period		3 years