Income Taxes (Narrative) (Details) $ in Millions	9 Months Ended
	Sep. 30, 2015 USD ($)
Income Taxes [Line Items]
Increase (decrease) non-current deferred tax liabilities	$ 141.0
IPL [Member]
Income Taxes [Line Items]
Increase (decrease) non-current deferred tax liabilities	78.5
WPL [Member]
Income Taxes [Line Items]
Increase (decrease) non-current deferred tax liabilities	$ 60.1