XML 155 R120.htm IDEA: XBRL DOCUMENT v2.4.1.9

Benefit Plans (Summary Of Performance Unit Activity) (Details) (Performance Units [Member], USD $) In Millions, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested [Roll Forward]
Nonvested, January 1 (in shares/awards)	65,912us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber	[1]	64,969us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber	[1]	42,996us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber	[1]
Granted (in shares/awards)	20,422us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod	[1]	22,201us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod	[1]	24,686us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod	[1]
Vested (in shares/awards)	(20,751)us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod	[1]	(19,760)us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod	[1]	0us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod	[1]
Forfeited (in shares/awards)	(1,918)us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod	[1]	(1,498)us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod	[1]	(2,713)us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod	[1]
Nonvested, December 31 (in shares/awards)	63,665us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber	[1]	65,912us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber	[1]	64,969us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber	[1]
Instrument valuation based on shares of common stock, number of shares	1lnt_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsInstrumentValuationBasedOnSharesOfCommonStockNumberOfShares
Performance multiplier range, lower	0.00%lnt_PerformanceUnitsAdjustmentForPerformanceMultiplierRangeMinimum
Performance multiplier range, upper	200.00%lnt_PerformanceUnitsAdjustmentForPerformanceMultiplierRangeMaximum
2011 Grant [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested [Roll Forward]
Vested (in shares/awards)	(20,751)us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod / us-gaap_AwardDateAxis = lnt_TwoThousandElevenGrantMember / us-gaap_AwardTypeAxis = lnt_PerformanceUnitsMember
Vested percentage of the target	147.50%lnt_VestedPercentageOfTarget / us-gaap_AwardDateAxis = lnt_TwoThousandElevenGrantMember / us-gaap_AwardTypeAxis = lnt_PerformanceUnitsMember
Cash payout value	1.2us-gaap_EmployeeBenefitsAndShareBasedCompensation / us-gaap_AwardDateAxis = lnt_TwoThousandElevenGrantMember / us-gaap_AwardTypeAxis = lnt_PerformanceUnitsMember
2010 Grant [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested [Roll Forward]
Vested (in shares/awards)			(19,760)us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod / us-gaap_AwardDateAxis = lnt_TwoThousandTenGrantMember / us-gaap_AwardTypeAxis = lnt_PerformanceUnitsMember
Vested percentage of the target			197.50%lnt_VestedPercentageOfTarget / us-gaap_AwardDateAxis = lnt_TwoThousandTenGrantMember / us-gaap_AwardTypeAxis = lnt_PerformanceUnitsMember
Cash payout value			1.3us-gaap_EmployeeBenefitsAndShareBasedCompensation / us-gaap_AwardDateAxis = lnt_TwoThousandTenGrantMember / us-gaap_AwardTypeAxis = lnt_PerformanceUnitsMember
[1] Unit amounts represent the target number of performance units. Each performance unit’s value is based on the average price of one share of Alliant Energy’s common stock on the grant date of the award. The actual payout for performance units is dependent upon actual performance and may range from zero to 200% of the target number of units.

X

- Definition

Performance Units Adjustment For Performance Multiplier Range Maximum

+ References

No definition available.

+ Details

Name:	lnt_PerformanceUnitsAdjustmentForPerformanceMultiplierRangeMaximum
Namespace Prefix:	lnt_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Performance Units Adjustment For Performance Multiplier Range Minimum

+ References

No definition available.

+ Details

Name:	lnt_PerformanceUnitsAdjustmentForPerformanceMultiplierRangeMinimum
Namespace Prefix:	lnt_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Instrument Valuation Based On Shares of Common Stock, Number of Shares

+ References

No definition available.

+ Details

Name:	lnt_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsInstrumentValuationBasedOnSharesOfCommonStockNumberOfShares
Namespace Prefix:	lnt_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Vested Percentage Of The Target

+ References

No definition available.

+ Details

Name:	lnt_VestedPercentageOfTarget
Namespace Prefix:	lnt_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Costs and payments related to employee benefits and equity-based compensation, such as pension expense and contributions, other postretirement benefits expense and payments, stock or unit options expense, and amortization of restricted stock or unit.

+ 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 (a)

-URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3602-108585

+ Details

Name:	us-gaap_EmployeeBenefitsAndShareBasedCompensation
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

X

- Definition

The number of equity-based payment instruments, excluding stock (or unit) options, that were forfeited during the reporting period.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (c)(1)(iv)(3)

-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

X

- Definition

The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (c)(2)(iii)(1)

-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

X

- Definition

The number of non-vested equity-based payment instruments, excluding stock (or unit) options, that validly exist and are outstanding as of the balance sheet date.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (c)(2)(i)-(ii)

-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

X

- Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

X

- Definition

The number of equity-based payment instruments, excluding stock (or unit) options, that vested during the reporting period.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (c)(2)(iii)(2)

-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

X

- Details

Name:	us-gaap_AwardDateAxis=lnt_TwoThousandElevenGrantMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_AwardDateAxis=lnt_TwoThousandTenGrantMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: