Benefit Plans (Expected Benefit Payments) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014
Defined Benefit Plan Disclosure [Line Items]
Expected benefit payments, 2015	$ 84.3
Expected benefit payments, 2016	88.3
Expected benefit payments, 2017	86.0
Expected benefit payments, 2018	89.8
Expected benefit payments, 2019	90.6
Expected benefit payments, 2020 - 2024	480.1
Defined Benefit Plans Qualified And Non Qualified Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Expected benefit payments, 2015	66.7
Expected benefit payments, 2016	71.5
Expected benefit payments, 2017	69.3
Expected benefit payments, 2018	72.9
Expected benefit payments, 2019	73.6
Expected benefit payments, 2020 - 2024	396.1
Other Postretirement Benefits Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Expected benefit payments, 2015	17.6
Expected benefit payments, 2016	16.8
Expected benefit payments, 2017	16.7
Expected benefit payments, 2018	16.9
Expected benefit payments, 2019	17.0
Expected benefit payments, 2020 - 2024	84.0
IPL [Member]
Defined Benefit Plan Disclosure [Line Items]
Expected benefit payments, 2015	37.8
Expected benefit payments, 2016	38.8
Expected benefit payments, 2017	40.3
Expected benefit payments, 2018	42.1
Expected benefit payments, 2019	41.9
Expected benefit payments, 2020 - 2024	225.2
IPL [Member] \| Defined Benefit Plans Qualified And Non Qualified Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Expected benefit payments, 2015	30.4
Expected benefit payments, 2016	31.6
Expected benefit payments, 2017	33.1
Expected benefit payments, 2018	34.9
Expected benefit payments, 2019	34.7
Expected benefit payments, 2020 - 2024	189.9
IPL [Member] \| Other Postretirement Benefits Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Expected benefit payments, 2015	7.4
Expected benefit payments, 2016	7.2
Expected benefit payments, 2017	7.2
Expected benefit payments, 2018	7.2
Expected benefit payments, 2019	7.2
Expected benefit payments, 2020 - 2024	35.3
WPL [Member]
Defined Benefit Plan Disclosure [Line Items]
Expected benefit payments, 2015	36.1
Expected benefit payments, 2016	35.0
Expected benefit payments, 2017	35.8
Expected benefit payments, 2018	37.1
Expected benefit payments, 2019	37.6
Expected benefit payments, 2020 - 2024	197.6
WPL [Member] \| Defined Benefit Plans Qualified And Non Qualified Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Expected benefit payments, 2015	28.4
Expected benefit payments, 2016	28.0
Expected benefit payments, 2017	28.8
Expected benefit payments, 2018	30.1
Expected benefit payments, 2019	30.5
Expected benefit payments, 2020 - 2024	163.4
WPL [Member] \| Other Postretirement Benefits Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Expected benefit payments, 2015	7.7
Expected benefit payments, 2016	7.0
Expected benefit payments, 2017	7.0
Expected benefit payments, 2018	7.0
Expected benefit payments, 2019	7.1
Expected benefit payments, 2020 - 2024	$ 34.2

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Amount of benefits from a defined benefit plan expected to be paid in the five fiscal years after the fifth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

+ 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=35743120&loc=d3e1928-114920

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Amount of benefits from a defined benefit plan expected to be paid in the next fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

+ References

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+ References

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Amount of benefits from a defined benefit plan expected to be paid in the fourth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

+ References

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Amount of benefits from a defined benefit plan expected to be paid in the third fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Amount of benefits from a defined benefit plan expected to be paid in the second fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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