Derivative Instruments (Notional Amounts Of Derivative Instruments) (Details) (Commodity [Member])	Mar. 31, 2013 MWh
Electricity (MWhs) [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	7,471,000
Electricity (MWhs) [Member] | IPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	3,011,000
Electricity (MWhs) [Member] | WPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	4,460,000
FTRs (MWs) [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	11,000
FTRs (MWs) [Member] | IPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	6,000
FTRs (MWs) [Member] | WPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	5,000
Natural Gas (Dths) [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	79,349,000
Natural Gas (Dths) [Member] | IPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	59,766,000
Natural Gas (Dths) [Member] | WPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	19,583,000
Coal (Tons) [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	2,215,000
Coal (Tons) [Member] | WPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	2,215,000
2013 [Member] | Electricity (MWhs) [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	3,431,000
2013 [Member] | Electricity (MWhs) [Member] | IPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	1,987,000
2013 [Member] | Electricity (MWhs) [Member] | WPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	1,444,000
2013 [Member] | FTRs (MWs) [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	11,000
2013 [Member] | FTRs (MWs) [Member] | IPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	6,000
2013 [Member] | FTRs (MWs) [Member] | WPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	5,000
2013 [Member] | Natural Gas (Dths) [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	66,884,000
2013 [Member] | Natural Gas (Dths) [Member] | IPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	52,116,000
2013 [Member] | Natural Gas (Dths) [Member] | WPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	14,768,000
2013 [Member] | Coal (Tons) [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	672,000
2013 [Member] | Coal (Tons) [Member] | WPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	672,000
2014 [Member] | Electricity (MWhs) [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	3,164,000
2014 [Member] | Electricity (MWhs) [Member] | IPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	1,024,000
2014 [Member] | Electricity (MWhs) [Member] | WPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	2,140,000
2014 [Member] | FTRs (MWs) [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	0
2014 [Member] | FTRs (MWs) [Member] | IPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	0
2014 [Member] | FTRs (MWs) [Member] | WPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	0
2014 [Member] | Natural Gas (Dths) [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	10,130,000
2014 [Member] | Natural Gas (Dths) [Member] | IPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	5,765,000
2014 [Member] | Natural Gas (Dths) [Member] | WPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	4,365,000
2014 [Member] | Coal (Tons) [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	981,000
2014 [Member] | Coal (Tons) [Member] | WPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	981,000
2015 [Member] | Electricity (MWhs) [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	876,000
2015 [Member] | Electricity (MWhs) [Member] | IPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	0
2015 [Member] | Electricity (MWhs) [Member] | WPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	876,000
2015 [Member] | FTRs (MWs) [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	0
2015 [Member] | FTRs (MWs) [Member] | IPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	0
2015 [Member] | FTRs (MWs) [Member] | WPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	0
2015 [Member] | Natural Gas (Dths) [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	1,880,000
2015 [Member] | Natural Gas (Dths) [Member] | IPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	1,430,000
2015 [Member] | Natural Gas (Dths) [Member] | WPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	450,000
2015 [Member] | Coal (Tons) [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	562,000
2015 [Member] | Coal (Tons) [Member] | WPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	562,000
2016 [Member] | Electricity (MWhs) [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	0
2016 [Member] | Electricity (MWhs) [Member] | IPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	0
2016 [Member] | Electricity (MWhs) [Member] | WPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	0
2016 [Member] | FTRs (MWs) [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	0
2016 [Member] | FTRs (MWs) [Member] | IPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	0
2016 [Member] | FTRs (MWs) [Member] | WPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	0
2016 [Member] | Natural Gas (Dths) [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	455,000
2016 [Member] | Natural Gas (Dths) [Member] | IPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	455,000
2016 [Member] | Natural Gas (Dths) [Member] | WPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	0
2016 [Member] | Coal (Tons) [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	0
2016 [Member] | Coal (Tons) [Member] | WPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	0