Benefit Plans (Expected Benefit Payments) (Details) (Scenario, Forecast [Member], USD $) In Millions, unless otherwise specified	Dec. 31, 2013
Defined Benefit Plan Disclosure [Line Items]
Expected benefit payments, 2014	$ 88.2
Expected benefit payments, 2015	84.7
Expected benefit payments, 2016	82.6
Expected benefit payments, 2017	84.1
Expected benefit payments, 2018	87.9
Expected benefit payments, 2019 - 2023	462.1
Defined Benefit Plans Qualified And Non Qualified Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Expected benefit payments, 2014	71.2
Expected benefit payments, 2015	68.0
Expected benefit payments, 2016	66.3
Expected benefit payments, 2017	67.8
Expected benefit payments, 2018	71.2
Expected benefit payments, 2019 - 2023	378.6
Other Postretirement Benefits Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Expected benefit payments, 2014	17.0
Expected benefit payments, 2015	16.7
Expected benefit payments, 2016	16.3
Expected benefit payments, 2017	16.3
Expected benefit payments, 2018	16.7
Expected benefit payments, 2019 - 2023	83.5
IPL [Member]
Defined Benefit Plan Disclosure [Line Items]
Expected benefit payments, 2014	39.9
Expected benefit payments, 2015	37.2
Expected benefit payments, 2016	38.4
Expected benefit payments, 2017	39.8
Expected benefit payments, 2018	41.6
Expected benefit payments, 2019 - 2023	215.8
IPL [Member] | Defined Benefit Plans Qualified And Non Qualified Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Expected benefit payments, 2014	32.2
Expected benefit payments, 2015	29.9
Expected benefit payments, 2016	31.3
Expected benefit payments, 2017	32.8
Expected benefit payments, 2018	34.4
Expected benefit payments, 2019 - 2023	180.4
IPL [Member] | Other Postretirement Benefits Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Expected benefit payments, 2014	7.7
Expected benefit payments, 2015	7.3
Expected benefit payments, 2016	7.1
Expected benefit payments, 2017	7.0
Expected benefit payments, 2018	7.2
Expected benefit payments, 2019 - 2023	35.4
WPL [Member]
Defined Benefit Plan Disclosure [Line Items]
Expected benefit payments, 2014	33.3
Expected benefit payments, 2015	34.2
Expected benefit payments, 2016	33.8
Expected benefit payments, 2017	35.0
Expected benefit payments, 2018	36.3
Expected benefit payments, 2019 - 2023	189.7
WPL [Member] | Defined Benefit Plans Qualified And Non Qualified Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Expected benefit payments, 2014	26.4
Expected benefit payments, 2015	27.2
Expected benefit payments, 2016	27.1
Expected benefit payments, 2017	28.3
Expected benefit payments, 2018	29.4
Expected benefit payments, 2019 - 2023	155.8
WPL [Member] | Other Postretirement Benefits Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Expected benefit payments, 2014	6.9
Expected benefit payments, 2015	7.0
Expected benefit payments, 2016	6.7
Expected benefit payments, 2017	6.7
Expected benefit payments, 2018	6.9
Expected benefit payments, 2019 - 2023	$ 33.9