Regulatory Matters Regulatory Matters (Tax Benefit Riders) (Details) (Alliant Energy and IPL [Member], USD $) In Millions, unless otherwise specified	3 Months Ended
Mar. 31, 2014
Electric tax benefit rider [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	$ 23.0
Gas tax benefit rider [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	3.0
Tax benefit riders [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	$ 26.0

The increase (decrease) during the reporting period in regulated liabilities. Regulated liabilities are created when regulatory agency permits an entity to defer revenues to the balance sheet.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 28

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3602-108585

Name:	us-gaap_IncreaseDecreaseInRegulatoryLiabilities
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration