XML 24 R48.htm IDEA: XBRL DOCUMENT
v3.2.0.727

Investments (Unconsolidated Equity Investments) (Details) - USD ($) $ in Millions | 3 Months Ended | 6 Months Ended
--- | --- | ---
Jun. 30, 2015 | Jun. 30, 2014 | Jun. 30, 2015 | Jun. 30, 2014
Schedule of Investments [Line Items] |  |  |  |
Equity (income) loss from unconsolidated investments, net | $ (11.3) | $ (11.3) | $ (17.8) | $ (22.7)
WPL [Member] |  |  |  |
Schedule of Investments [Line Items] |  |  |  |
Equity (income) loss from unconsolidated investments, net | (11.3) | (11.4) | (19.1) | (22.8)
ATC [Member] |  |  |  |
Schedule of Investments [Line Items] |  |  |  |
Equity (income) loss from unconsolidated investments, net | (10.9) | (11.1) | (18.7) | (22.3)
ATC [Member] | WPL [Member] |  |  |  |
Schedule of Investments [Line Items] |  |  |  |
Equity (income) loss from unconsolidated investments, net | (10.9) | (11.1) | (18.7) | (22.3)
Other [Member] |  |  |  |
Schedule of Investments [Line Items] |  |  |  |
Equity (income) loss from unconsolidated investments, net | (0.4) | (0.2) | 0.9 | (0.4)
Other [Member] | WPL [Member] |  |  |  |
Schedule of Investments [Line Items] |  |  |  |
Equity (income) loss from unconsolidated investments, net | $ (0.4) | $ (0.3) | $ (0.4) | $ (0.5)

X
- Definition This item represents the entity's proportionate share for the period of the net income (loss) of its investee (such as unconsolidated subsidiaries and joint ventures) to which the equity method of accounting is applied. This item includes income or expense related to stock-based compensation based on the investor's grant of stock to employees of an equity method investee. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3602-108585 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 323 -SubTopic 10 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=35755396&loc=d3e33749-111570 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 225 -SubTopic 10 -Section S99 -Paragraph 2 -Subparagraph (SX 210.5-03.12) -URI http://asc.fasb.org/extlink&oid=26872669&loc=d3e20235-122688 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 9 -Article 5 Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 04 -Paragraph 11 -Article 7 + Details
Name: | us-gaap_IncomeLossFromEquityMethodInvestments
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
Name: | us-gaap_ScheduleOfEquityMethodInvestmentsLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | dei_LegalEntityAxis=lnt_WplMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis=lnt_AmericanTransmissionCompanyLlcAtcMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis=lnt_OtherEquityMethodInvestmentsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |