Income Taxes (Narrative) (Details) $ in Millions	9 Months Ended
	Sep. 30, 2017 USD ($)
Income Taxes [Line Items]
Increase in deferred tax liabilities	$ 204.5
IPL [Member]
Income Taxes [Line Items]
Increase in deferred tax liabilities	131.7
WPL [Member]
Income Taxes [Line Items]
Increase in deferred tax liabilities	$ 63.6