XML 57 R86.htm IDEA: XBRL DOCUMENT v2.4.1.9

Debt (Credit Facilities) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Commercial paper:
Amount outstanding	$ 141.3us-gaap_CommercialPaper	$ 279.4us-gaap_CommercialPaper
Weighted average interest rates	0.40%us-gaap_ShortTermDebtWeightedAverageInterestRate	0.20%us-gaap_ShortTermDebtWeightedAverageInterestRate
Weighted average remaining maturity	4 days	4 days
Available credit facility capacity	858.7us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity	720.6us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity
IPL [Member]
Commercial paper:
Amount outstanding	0us-gaap_CommercialPaper / dei_LegalEntityAxis = lnt_IplMember	0us-gaap_CommercialPaper / dei_LegalEntityAxis = lnt_IplMember
Available credit facility capacity	300.0us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity / dei_LegalEntityAxis = lnt_IplMember	300.0us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity / dei_LegalEntityAxis = lnt_IplMember
WPL [Member]
Commercial paper:
Amount outstanding	0us-gaap_CommercialPaper / dei_LegalEntityAxis = lnt_WplMember	183.7us-gaap_CommercialPaper / dei_LegalEntityAxis = lnt_WplMember
Weighted average interest rates		0.10%us-gaap_ShortTermDebtWeightedAverageInterestRate / dei_LegalEntityAxis = lnt_WplMember
Weighted average remaining maturity		6 days
Available credit facility capacity	$ 400.0us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity / dei_LegalEntityAxis = lnt_WplMember	$ 216.3us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity / dei_LegalEntityAxis = lnt_WplMember

X

- Details

Name:	lnt_CommercialPaperAbstract
Namespace Prefix:	lnt_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Short Term Debt Weighted Average Remaining Maturity

+ References

No definition available.

+ Details

Name:	lnt_ShortTermDebtWeightedAverageRemainingMaturity
Namespace Prefix:	lnt_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Carrying value as of the balance sheet date of short-term borrowings using unsecured obligations issued by banks, corporations and other borrowers to investors. The maturities of these money market securities generally do not exceed 270 days.

+ References

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 16

-Article 7



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 210.5-02.19(a)(3))

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682



Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 210

-Section S99

-Paragraph 1

-Subparagraph (SX 210.9-03.13(2))

-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878



Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 19

-Subparagraph a(3)

-Article 5



Reference 5: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 13

-Subparagraph 2

-Article 9

+ Details

Name:	us-gaap_CommercialPaper
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

X

- Definition

Amount of borrowing capacity currently available under the credit facility (current borrowing capacity less the amount of borrowings outstanding).

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.19(b),22(b))

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682



Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 19, 22

-Article 5

+ Details

Name:	us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

X

- Definition

Weighted average interest rate of short-term debt outstanding.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.19(b))

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682



Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 19

-Subparagraph b

-Article 5

+ Details

Name:	us-gaap_ShortTermDebtWeightedAverageInterestRate
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

X

- Details

Name:	dei_LegalEntityAxis=lnt_IplMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	dei_LegalEntityAxis=lnt_WplMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: