Summary Of Significant Accounting Policies (Narrative) (Details) $ in Millions		12 Months Ended
		Dec. 31, 2015 USD ($) customer $ / unit MW	Dec. 31, 2014 USD ($)
Asset Impairments:
Non-regulated Generation, net | $	[1]	$ 229.3	$ 240.1
IPL [Member]
General:
Generation and distribution of steam, number of customers served (in customers) | customer		2
Property, Plant and Equipment:
AFUDC accrual recorded, percentage of estimated CWIP		100.00%
Operating Revenues:
Estimated recovery of overaccrued operating revenue, reflected on customer billing, maximum period		2 years
WPL [Member]
Property, Plant and Equipment:
AFUDC accrual recorded, percentage of estimated CWIP		50.00%
AFUDC rates, projects with approval		100.00%
Operating Revenues:
Final settlement recovery of overaccrued operating revenue, reflected on customer billing, maximum period		2 years
Sheboygan Falls Energy Facility [Member]
General:
Fossil-fueled EGU capacity (in megawatts) | MW		347
Capital lease, lease term		20 years
Franklin County Wind Farm [Member]
General:
Wind EGU capacity (in megawatts) | MW		99
Asset Impairments:
Non-regulated Generation, net | $		$ 130.0
Customer Billing And Information System [Member]
Property, Plant and Equipment:
Property, plant and equipment, useful life		12 years
Software [Member]
Property, Plant and Equipment:
Property, plant and equipment, useful life		5 years
Minimum [Member]
Asset Impairments:
Average forward electricity price (in dollars per MWh) | $ / unit		2
Maximum [Member]
Asset Impairments:
Average forward electricity price (in dollars per MWh) | $ / unit		3

[1] Less accumulated depreciation of $59.0 million and $49.5 million for Alliant Energy as of December 31, 2015 and 2014, respectively.