Income Taxes (Narrative) (Details) $ in Millions	6 Months Ended
	Jun. 30, 2015 USD ($)
Income Taxes [Line Items]
Increase (decrease) non-current deferred tax liabilities	$ 128.0
IPL [Member]
Income Taxes [Line Items]
Increase (decrease) non-current deferred tax liabilities	77.4
WPL [Member]
Income Taxes [Line Items]
Increase (decrease) non-current deferred tax liabilities	$ 44.9