XML 20 R39.htm IDEA: XBRL DOCUMENT
v2.4.0.6

Summary Of Significant Accounting Policies (Narrative) (Details) (USD $) In Millions, unless otherwise specified | 3 Months Ended
--- | ---
Mar. 31, 2013 | Mar. 31, 2012
Public Utility, Property, Plant and Equipment [Line Items] |  |
Regulatory liabilities | $ 20.4 | $ (26.5)
Alliant Energy and IPL [Member] | IPL's tax benefit riders [Member] |  |
Public Utility, Property, Plant and Equipment [Line Items] |  |
Regulatory liabilities | 20.7 |
IPL [Member] |  |
Public Utility, Property, Plant and Equipment [Line Items] |  |
Regulatory liabilities | 14.7 | (33.6)
IPL [Member] | Electric tax benefit rider [Member] |  |
Public Utility, Property, Plant and Equipment [Line Items] |  |
Regulatory liabilities | 18.3 |
IPL [Member] | Gas tax benefit rider [Member] |  |
Public Utility, Property, Plant and Equipment [Line Items] |  |
Regulatory liabilities | $ 2.4 |

X
- Definition 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. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 28 -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. Reference 2: 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=6943989&loc=d3e3602-108585 + Details
Name: | us-gaap_IncreaseDecreaseInRegulatoryLiabilities
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Details
Name: | us-gaap_PublicUtilityPropertyPlantAndEquipmentLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration