XML 38 R71.htm IDEA: XBRL DOCUMENT
v2.4.0.6

Fair Value Measurements (Fair Value Of Financial Instruments) (Details) (USD $) In Millions, unless otherwise specified | Mar. 31, 2013 | Dec. 31, 2012
--- | --- | ---
Assets: |  |
Derivative assets | $ 23.6 | $ 26.2
Deferred proceeds (sales of receivables) | 122.1 | 66.8
Capitalization and liabilities: |  |
Long-term debt (including current maturities) | 3,806.5 | 3,860.5
Cumulative preferred stock | 200.0 | 145.1
Cumulative preferred stock | 201.8 |
Cumulative preferred stock | 0 | 60.0
Cumulative preferred stock |  | 212.6
Derivative liabilities | 17.1 | 40.4
IPL [Member] |  |
Assets: |  |
Derivative assets | 12.5 | 17.5
Deferred proceeds (sales of receivables) | 122.1 | 66.8
Capitalization and liabilities: |  |
Long-term debt (including current maturities) | 1,643.8 | 1,679.9
Cumulative preferred stock | 200.0 | 145.1
Cumulative preferred stock | 201.8 | 151.8
Derivative liabilities | 6.1 | 16.1
WPL [Member] |  |
Assets: |  |
Derivative assets | 11.1 | 8.7
Capitalization and liabilities: |  |
Long-term debt (including current maturities) | 1,691.6 | 1,713.3
Cumulative preferred stock | 0 | 60.0
Cumulative preferred stock | 0 | 60.8
Derivative liabilities | 11.0 | 24.3
Carrying Amount [Member] |  |
Assets: |  |
Derivative assets | 23.6 | 26.2
Deferred proceeds (sales of receivables) | 122.1 | 66.8
Capitalization and liabilities: |  |
Long-term debt (including current maturities) | 3,123.4 | 3,138.1
Cumulative preferred stock | 200.0 |
Cumulative preferred stock |  | 205.1
Derivative liabilities | 17.1 | 40.4
Carrying Amount [Member] | IPL [Member] |  |
Assets: |  |
Derivative assets | 12.5 | 17.5
Deferred proceeds (sales of receivables) | 122.1 | 66.8
Capitalization and liabilities: |  |
Long-term debt (including current maturities) | 1,344.5 | 1,359.5
Cumulative preferred stock | 200.0 | 145.1
Derivative liabilities | 6.1 | 16.1
Carrying Amount [Member] | WPL [Member] |  |
Assets: |  |
Derivative assets | 11.1 | 8.7
Deferred proceeds (sales of receivables) | 0 | 0
Capitalization and liabilities: |  |
Long-term debt (including current maturities) | 1,331.7 | 1,331.5
Cumulative preferred stock | 0 | 60.0
Derivative liabilities | 11.0 | 24.3
Fair Value [Member] |  |
Assets: |  |
Derivative assets | 23.6 | 26.2
Deferred proceeds (sales of receivables) | 122.1 | 66.8
Capitalization and liabilities: |  |
Long-term debt (including current maturities) | 3,806.5 | 3,860.5
Cumulative preferred stock | 201.8 |
Cumulative preferred stock |  | 212.6
Derivative liabilities | 17.1 | 40.4
Fair Value [Member] | IPL [Member] |  |
Assets: |  |
Derivative assets | 12.5 | 17.5
Deferred proceeds (sales of receivables) | 122.1 | 66.8
Capitalization and liabilities: |  |
Long-term debt (including current maturities) | 1,643.8 | 1,679.9
Cumulative preferred stock | 201.8 | 151.8
Derivative liabilities | 6.1 | 16.1
Fair Value [Member] | WPL [Member] |  |
Assets: |  |
Derivative assets | 11.1 | 8.7
Deferred proceeds (sales of receivables) | 0 | 0
Capitalization and liabilities: |  |
Long-term debt (including current maturities) | 1,691.6 | 1,713.3
Cumulative preferred stock | 0 | 60.8
Derivative liabilities | $ 11.0 | $ 24.3

X
- Details
Name: | lnt_CapitalizationAndLiabilitiesAbstract
Namespace Prefix: | lnt_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Fair value of deferred proceeds of receivables sold + References No definition available. + Details
Name: | lnt_FairValueOfDeferredProceedsOfReceivablesSold
Namespace Prefix: | lnt_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Preferred Stock Fair Value + References No definition available. + Details
Name: | lnt_PreferredStockFairValue
Namespace Prefix: | lnt_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition The carrying value (book value) of preferred stock of subsidiaries. + References No definition available. + Details
Name: | lnt_TemporaryEquityAndPreferredStockCarryingAmount
Namespace Prefix: | lnt_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Cumulative preferred stock of subsidiaries, fair value. + References No definition available. + Details
Name: | lnt_TemporaryEquityAndPreferredStockFairValue
Namespace Prefix: | lnt_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Temporary Equity Fair Value + References No definition available. + Details
Name: | lnt_TemporaryEquityFairValue
Namespace Prefix: | lnt_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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

X
- Definition This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 825 -SubTopic 10 -Section 50 -Paragraph 10 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=7491637&loc=d3e13433-108611 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 825 -SubTopic 10 -Section 50 -Paragraph 12 -URI http://asc.fasb.org/extlink&oid=7491637&loc=d3e13476-108611 + Details
Name: | us-gaap_DebtInstrumentFairValue
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Fair value of derivative asset, presented on a gross basis even when the derivative instrument is subject to master netting arrangements and qualifies for net presentation in the statement of financial position. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 133 -Paragraph 205G -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 Statement of Financial Accounting Standard (FAS) -Number 133 -Paragraph 44C -Subparagraph a -Clause 1 -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 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 4B -Subparagraph (a),(c) -URI http://asc.fasb.org/extlink&oid=7476318&loc=SL5624163-113959 + Details
Name: | us-gaap_DerivativeFairValueOfDerivativeAsset
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Fair value of derivative liability, presented on a gross basis even when the derivative instrument is subject to master netting arrangements and qualifies for net presentation in the statement of financial position. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 133 -Paragraph 205G -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 Statement of Financial Accounting Standard (FAS) -Number 133 -Paragraph 44C -Subparagraph a -Clause 1 -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 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 4B -Subparagraph (a),(c) -URI http://asc.fasb.org/extlink&oid=7476318&loc=SL5624163-113959 + Details
Name: | us-gaap_DerivativeFairValueOfDerivativeLiability
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Carrying amount of long-term debt, net of unamortized discount or premium, including current and noncurrent amounts. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03.16) -URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 16 -Article 9 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 16 -Article 7 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 20, 22 -Article 5 Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.22) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 6: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03.16) -URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910 + Details
Name: | us-gaap_LongTermDebt
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Aggregate par or stated value of issued nonredeemable preferred stock (or preferred stock redeemable solely at the option of the issuer). This item includes treasury stock repurchased by the entity. Note: elements for number of nonredeemable preferred shares, par value and other disclosure concepts are in another section within stockholders' equity. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 29 -Article 5 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.28) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher AICPA -Name Accounting Principles Board Opinion (APB) -Number 12 -Paragraph 10 -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 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 129 -Paragraph 2, 3, 4, 5, 6, 7, 8 -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 5: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 04 -Article 3 Reference 6: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 505 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.3-04) -URI http://asc.fasb.org/extlink&oid=6959260&loc=d3e187085-122770 + Details
Name: | us-gaap_PreferredStockValue
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Carrying amount, attributable to parent, of an entity's issued and outstanding stock which is not included within permanent equity. Temporary equity is a security with redemption features that are outside the control of the issuer, is not classified as an asset or liability in conformity with GAAP, and is not mandatorily redeemable. Includes any type of security that is redeemable at a fixed or determinable price or on a fixed or determinable date or dates, is redeemable at the option of the holder, or has conditions for redemption which are not solely within the control of the issuer. Includes stock with a put option held by an ESOP and stock redeemable by a holder only in the event of a change in control of the issuer. + References No definition available. + Details
Name: | us-gaap_TemporaryEquityCarryingAmountAttributableToParent
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant