XML 54 R134.htm IDEA: XBRL DOCUMENT
v2.4.1.9

Derivative Instruments (Gains And Losses From Derivative Instruments) (Details) (Commodity Contracts [Member], USD $) In Millions, unless otherwise specified | 12 Months Ended
--- | ---
Dec. 31, 2014 | Dec. 31, 2013 | Dec. 31, 2012
Regulatory Assets [Member] |  |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |  |
Changes in unrealized gains (losses) from derivative instruments | $ (13.8)us-gaap_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsGainLossNet / us-gaap_BalanceSheetLocationAxis = lnt_RegulatoryAssetsMember / us-gaap_FairValueByAssetClassAxis = us-gaap_CommodityContractMember | $ (14.7)us-gaap_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsGainLossNet / us-gaap_BalanceSheetLocationAxis = lnt_RegulatoryAssetsMember / us-gaap_FairValueByAssetClassAxis = us-gaap_CommodityContractMember | $ (37.9)us-gaap_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsGainLossNet / us-gaap_BalanceSheetLocationAxis = lnt_RegulatoryAssetsMember / us-gaap_FairValueByAssetClassAxis = us-gaap_CommodityContractMember
Regulatory Assets [Member] | IPL [Member] |  |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |  |
Changes in unrealized gains (losses) from derivative instruments | (5.8)us-gaap_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsGainLossNet / us-gaap_BalanceSheetLocationAxis = lnt_RegulatoryAssetsMember / us-gaap_FairValueByAssetClassAxis = us-gaap_CommodityContractMember / dei_LegalEntityAxis = lnt_IplMember | (6.6)us-gaap_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsGainLossNet / us-gaap_BalanceSheetLocationAxis = lnt_RegulatoryAssetsMember / us-gaap_FairValueByAssetClassAxis = us-gaap_CommodityContractMember / dei_LegalEntityAxis = lnt_IplMember | (16.8)us-gaap_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsGainLossNet / us-gaap_BalanceSheetLocationAxis = lnt_RegulatoryAssetsMember / us-gaap_FairValueByAssetClassAxis = us-gaap_CommodityContractMember / dei_LegalEntityAxis = lnt_IplMember
Regulatory Assets [Member] | WPL [Member] |  |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |  |
Changes in unrealized gains (losses) from derivative instruments | (8.0)us-gaap_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsGainLossNet / us-gaap_BalanceSheetLocationAxis = lnt_RegulatoryAssetsMember / us-gaap_FairValueByAssetClassAxis = us-gaap_CommodityContractMember / dei_LegalEntityAxis = lnt_WplMember | (8.1)us-gaap_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsGainLossNet / us-gaap_BalanceSheetLocationAxis = lnt_RegulatoryAssetsMember / us-gaap_FairValueByAssetClassAxis = us-gaap_CommodityContractMember / dei_LegalEntityAxis = lnt_WplMember | (21.1)us-gaap_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsGainLossNet / us-gaap_BalanceSheetLocationAxis = lnt_RegulatoryAssetsMember / us-gaap_FairValueByAssetClassAxis = us-gaap_CommodityContractMember / dei_LegalEntityAxis = lnt_WplMember
Regulatory Liabilities [Member] |  |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |  |
Changes in unrealized gains (losses) from derivative instruments | 37.4 us-gaap_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsGainLossNet / us-gaap_BalanceSheetLocationAxis = lnt_RegulatoryLiabilitiesMember / us-gaap_FairValueByAssetClassAxis = us-gaap_CommodityContractMember | 22.2 us-gaap_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsGainLossNet / us-gaap_BalanceSheetLocationAxis = lnt_RegulatoryLiabilitiesMember / us-gaap_FairValueByAssetClassAxis = us-gaap_CommodityContractMember | 20.3 us-gaap_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsGainLossNet / us-gaap_BalanceSheetLocationAxis = lnt_RegulatoryLiabilitiesMember / us-gaap_FairValueByAssetClassAxis = us-gaap_CommodityContractMember
Regulatory Liabilities [Member] | IPL [Member] |  |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |  |
Changes in unrealized gains (losses) from derivative instruments | 10.2 us-gaap_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsGainLossNet / us-gaap_BalanceSheetLocationAxis = lnt_RegulatoryLiabilitiesMember / us-gaap_FairValueByAssetClassAxis = us-gaap_CommodityContractMember / dei_LegalEntityAxis = lnt_IplMember | 11.8 us-gaap_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsGainLossNet / us-gaap_BalanceSheetLocationAxis = lnt_RegulatoryLiabilitiesMember / us-gaap_FairValueByAssetClassAxis = us-gaap_CommodityContractMember / dei_LegalEntityAxis = lnt_IplMember | 13.5 us-gaap_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsGainLossNet / us-gaap_BalanceSheetLocationAxis = lnt_RegulatoryLiabilitiesMember / us-gaap_FairValueByAssetClassAxis = us-gaap_CommodityContractMember / dei_LegalEntityAxis = lnt_IplMember
Regulatory Liabilities [Member] | WPL [Member] |  |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |  |
Changes in unrealized gains (losses) from derivative instruments | $ 27.2 us-gaap_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsGainLossNet / us-gaap_BalanceSheetLocationAxis = lnt_RegulatoryLiabilitiesMember / us-gaap_FairValueByAssetClassAxis = us-gaap_CommodityContractMember / dei_LegalEntityAxis = lnt_WplMember | $ 10.4 us-gaap_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsGainLossNet / us-gaap_BalanceSheetLocationAxis = lnt_RegulatoryLiabilitiesMember / us-gaap_FairValueByAssetClassAxis = us-gaap_CommodityContractMember / dei_LegalEntityAxis = lnt_WplMember | $ 6.8 us-gaap_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsGainLossNet / us-gaap_BalanceSheetLocationAxis = lnt_RegulatoryLiabilitiesMember / us-gaap_FairValueByAssetClassAxis = us-gaap_CommodityContractMember / dei_LegalEntityAxis = lnt_WplMember

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

X
- Definition Amount of realized and unrealized gain (loss) of derivative instruments not designated or qualifying as hedging instruments. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 4C -Subparagraph (e) -URI http://asc.fasb.org/extlink&oid=35706170&loc=SL5624171-113959 + Details
Name: | us-gaap_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsGainLossNet
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration