Benefit Plans (Expected Benefit Payments) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012
Defined Benefit Plan Disclosure [Line Items]
Expected benefit payments, 2013	$ 78.5
Expected benefit payments, 2014	80.9
Expected benefit payments, 2015	84.8
Expected benefit payments, 2016	83.0
Expected benefit payments, 2017	85.8
Expected benefit payments, 2018 - 2022	458.3
Defined Benefit Plans Qualified And Non Qualified Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Expected benefit payments, 2013	61.9
Expected benefit payments, 2014	64.7
Expected benefit payments, 2015	68.5
Expected benefit payments, 2016	66.6
Expected benefit payments, 2017	69.2
Expected benefit payments, 2018 - 2022	374.1
Other Postretirement Benefits Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Expected benefit payments, 2013	16.6
Expected benefit payments, 2014	16.2
Expected benefit payments, 2015	16.3
Expected benefit payments, 2016	16.4
Expected benefit payments, 2017	16.6
Expected benefit payments, 2018 - 2022	84.2
IPL [Member]
Defined Benefit Plan Disclosure [Line Items]
Expected benefit payments, 2013	36.5
Expected benefit payments, 2014	37.6
Expected benefit payments, 2015	39.2
Expected benefit payments, 2016	38.1
Expected benefit payments, 2017	40.7
Expected benefit payments, 2018 - 2022	212.1
IPL [Member] \| Defined Benefit Plans Qualified And Non Qualified Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Expected benefit payments, 2013	15.9
Expected benefit payments, 2014	16.9
Expected benefit payments, 2015	17.9
Expected benefit payments, 2016	18.9
Expected benefit payments, 2017	20.0
Expected benefit payments, 2018 - 2022	116.0
IPL [Member] \| Directly Assigned Defined Benefit Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Expected benefit payments, 2013	12.6
Expected benefit payments, 2014	13.4
Expected benefit payments, 2015	14.1
Expected benefit payments, 2016	12.1
Expected benefit payments, 2017	13.5
Expected benefit payments, 2018 - 2022	60.2
IPL [Member] \| Other Postretirement Benefits Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Expected benefit payments, 2013	8.0
Expected benefit payments, 2014	7.3
Expected benefit payments, 2015	7.2
Expected benefit payments, 2016	7.1
Expected benefit payments, 2017	7.2
Expected benefit payments, 2018 - 2022	35.9
WPL [Member]
Defined Benefit Plan Disclosure [Line Items]
Expected benefit payments, 2013	31.2
Expected benefit payments, 2014	31.9
Expected benefit payments, 2015	34.2
Expected benefit payments, 2016	33.5
Expected benefit payments, 2017	34.3
Expected benefit payments, 2018 - 2022	186.0
WPL [Member] \| Defined Benefit Plans Qualified And Non Qualified Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Expected benefit payments, 2013	14.4
Expected benefit payments, 2014	15.2
Expected benefit payments, 2015	16.1
Expected benefit payments, 2016	17.0
Expected benefit payments, 2017	18.0
Expected benefit payments, 2018 - 2022	108.7
WPL [Member] \| Directly Assigned Defined Benefit Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Expected benefit payments, 2013	10.5
Expected benefit payments, 2014	10.2
Expected benefit payments, 2015	11.4
Expected benefit payments, 2016	9.8
Expected benefit payments, 2017	9.5
Expected benefit payments, 2018 - 2022	43.0
WPL [Member] \| Other Postretirement Benefits Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Expected benefit payments, 2013	6.3
Expected benefit payments, 2014	6.5
Expected benefit payments, 2015	6.7
Expected benefit payments, 2016	6.7
Expected benefit payments, 2017	6.8
Expected benefit payments, 2018 - 2022	$ 34.3

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Amount of benefits expected to be paid in the five fiscal years after the fifth fiscal year following the latest fiscal year from a defined benefit plan.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 715

-SubTopic 20

-Section 50

-Paragraph 1

-Subparagraph (f)

-URI http://asc.fasb.org/extlink&oid=21915506&loc=d3e1928-114920

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- Definition

Amount of benefits expected to be paid in the next fiscal year following the latest fiscal year from a defined benefit plan.

+ References

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Amount of benefits expected to be paid in the fifth fiscal year following the latest fiscal year from a defined benefit plan.

+ References

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Amount of benefits expected to be paid in the fourth fiscal year following the latest fiscal year from a defined benefit plan.

+ References

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Amount of benefits expected to be paid in the third fiscal year following the latest fiscal year from a defined benefit plan.

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Amount of benefits expected to be paid in the second fiscal year following the latest fiscal year from a defined benefit plan.

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