Derivative Instruments (Notional Amounts Of Derivative Instruments) (Details) (Commodity [Member])	Sep. 30, 2013 MWh
Electricity (MWhs) [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	13,221,000
Electricity (MWhs) [Member] | IPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	2,758,000
Electricity (MWhs) [Member] | WPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	10,463,000
FTRs (MWs) [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	35,000
FTRs (MWs) [Member] | IPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	22,000
FTRs (MWs) [Member] | WPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	13,000
Natural Gas (Dths) [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	72,553,000
Natural Gas (Dths) [Member] | IPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	55,967,000
Natural Gas (Dths) [Member] | WPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	16,586,000
Coal (Tons) [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	5,303,000
Coal (Tons) [Member] | IPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	814,000
Coal (Tons) [Member] | WPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	4,489,000
2013 [Member] | Electricity (MWhs) [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	1,460,000
2013 [Member] | Electricity (MWhs) [Member] | IPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	835,000
2013 [Member] | Electricity (MWhs) [Member] | WPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	625,000
2013 [Member] | FTRs (MWs) [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	13,000
2013 [Member] | FTRs (MWs) [Member] | IPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	8,000
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)	30,852,000
2013 [Member] | Natural Gas (Dths) [Member] | IPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	23,908,000
2013 [Member] | Natural Gas (Dths) [Member] | WPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	6,944,000
2013 [Member] | Coal (Tons) [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	239,000
2013 [Member] | Coal (Tons) [Member] | IPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	15,000
2013 [Member] | Coal (Tons) [Member] | WPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	224,000
2014 [Member] | Electricity (MWhs) [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	5,625,000
2014 [Member] | Electricity (MWhs) [Member] | IPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	1,923,000
2014 [Member] | Electricity (MWhs) [Member] | WPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	3,702,000
2014 [Member] | FTRs (MWs) [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	22,000
2014 [Member] | FTRs (MWs) [Member] | IPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	14,000
2014 [Member] | FTRs (MWs) [Member] | WPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	8,000
2014 [Member] | Natural Gas (Dths) [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	32,518,000
2014 [Member] | Natural Gas (Dths) [Member] | IPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	24,001,000
2014 [Member] | Natural Gas (Dths) [Member] | WPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	8,517,000
2014 [Member] | Coal (Tons) [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	1,591,000
2014 [Member] | Coal (Tons) [Member] | IPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	270,000
2014 [Member] | Coal (Tons) [Member] | WPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	1,321,000
2015 [Member] | Electricity (MWhs) [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	2,190,000
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)	2,190,000
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)	7,544,000
2015 [Member] | Natural Gas (Dths) [Member] | IPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	6,419,000
2015 [Member] | Natural Gas (Dths) [Member] | WPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	1,125,000
2015 [Member] | Coal (Tons) [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	936,000
2015 [Member] | Coal (Tons) [Member] | IPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	0
2015 [Member] | Coal (Tons) [Member] | WPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	936,000
2016 [Member] | Electricity (MWhs) [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	1,318,000
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)	1,318,000
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)	1,639,000
2016 [Member] | Natural Gas (Dths) [Member] | IPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	1,639,000
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)	955,000
2016 [Member] | Coal (Tons) [Member] | IPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	216,000
2016 [Member] | Coal (Tons) [Member] | WPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	739,000
2017 [Member] | Electricity (MWhs) [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	1,314,000
2017 [Member] | Electricity (MWhs) [Member] | IPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	0
2017 [Member] | Electricity (MWhs) [Member] | WPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	1,314,000
2017 [Member] | FTRs (MWs) [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	0
2017 [Member] | FTRs (MWs) [Member] | IPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	0
2017 [Member] | FTRs (MWs) [Member] | WPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	0
2017 [Member] | Natural Gas (Dths) [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	0
2017 [Member] | Natural Gas (Dths) [Member] | IPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	0
2017 [Member] | Natural Gas (Dths) [Member] | WPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	0
2017 [Member] | Coal (Tons) [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	868,000
2017 [Member] | Coal (Tons) [Member] | IPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	129,000
2017 [Member] | Coal (Tons) [Member] | WPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	739,000
2018 [Member] | Electricity (MWhs) [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	1,314,000
2018 [Member] | Electricity (MWhs) [Member] | IPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	0
2018 [Member] | Electricity (MWhs) [Member] | WPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	1,314,000
2018 [Member] | FTRs (MWs) [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	0
2018 [Member] | FTRs (MWs) [Member] | IPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	0
2018 [Member] | FTRs (MWs) [Member] | WPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	0
2018 [Member] | Natural Gas (Dths) [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	0
2018 [Member] | Natural Gas (Dths) [Member] | IPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	0
2018 [Member] | Natural Gas (Dths) [Member] | WPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	0
2018 [Member] | Coal (Tons) [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	714,000
2018 [Member] | Coal (Tons) [Member] | IPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	184,000
2018 [Member] | Coal (Tons) [Member] | WPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs/MWs/Dths/Tons)	530,000