Income Taxes (Narrative) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2014
Income Tax [Line Items]
Increase (decrease) non-current deferred tax liabilities	$ 29.0
Deferred income tax assets [Member]
Income Tax [Line Items]
Increase (decrease) current deferred tax assets	(22.9)
IPL [Member]
Income Tax [Line Items]
Increase (decrease) non-current deferred tax liabilities	23.0
IPL [Member] | Deferred income tax assets [Member]
Income Tax [Line Items]
Increase (decrease) current deferred tax assets	(9.8)
WPL [Member]
Income Tax [Line Items]
Increase (decrease) non-current deferred tax liabilities	4.9
WPL [Member] | Deferred income tax assets [Member]
Income Tax [Line Items]
Increase (decrease) current deferred tax assets	$ (10.7)