Income Taxes (Narrative) (Details) $ in Millions	9 Months Ended
	Sep. 30, 2016 USD ($)
Income Taxes [Line Items]
Increase (decrease) in deferred tax liabilities	$ 149.4
IPL [Member]
Income Taxes [Line Items]
Increase (decrease) in deferred tax liabilities	115.6
WPL [Member]
Income Taxes [Line Items]
Increase (decrease) in deferred tax liabilities	$ 103.4