Income Taxes (Narrative) (Details) $ in Millions	6 Months Ended
	Jun. 30, 2016 USD ($)
Income Taxes [Line Items]
Increase (decrease) in non-current deferred tax liabilities	$ 92.9
IPL [Member]
Income Taxes [Line Items]
Increase (decrease) in non-current deferred tax liabilities	62.1
WPL [Member]
Income Taxes [Line Items]
Increase (decrease) in non-current deferred tax liabilities	$ 44.1