Derivative Instruments (Notional Amounts Of Derivative Instruments) (Details) (Commodity [Member])	Mar. 31, 2012
Electricity (MWhs) [Member]
Notional Unit Amount Of Derivatives	8,033,000
Electricity (MWhs) [Member] | IPL [Member]
Notional Unit Amount Of Derivatives	4,212,000
Electricity (MWhs) [Member] | WPL [Member]
Notional Unit Amount Of Derivatives	3,821,000
FTRs (MWs) [Member]
Notional Unit Amount Of Derivatives	8,000
FTRs (MWs) [Member] | IPL [Member]
Notional Unit Amount Of Derivatives	5,000
FTRs (MWs) [Member] | WPL [Member]
Notional Unit Amount Of Derivatives	3,000
Natural Gas (Dths) [Member]
Notional Unit Amount Of Derivatives	66,563,000
Natural Gas (Dths) [Member] | IPL [Member]
Notional Unit Amount Of Derivatives	36,948,000
Natural Gas (Dths) [Member] | WPL [Member]
Notional Unit Amount Of Derivatives	29,615,000
2012 [Member] | Electricity (MWhs) [Member]
Notional Unit Amount Of Derivatives	3,994,000
2012 [Member] | Electricity (MWhs) [Member] | IPL [Member]
Notional Unit Amount Of Derivatives	2,416,000
2012 [Member] | Electricity (MWhs) [Member] | WPL [Member]
Notional Unit Amount Of Derivatives	1,578,000
2012 [Member] | FTRs (MWs) [Member]
Notional Unit Amount Of Derivatives	8,000
2012 [Member] | FTRs (MWs) [Member] | IPL [Member]
Notional Unit Amount Of Derivatives	5,000
2012 [Member] | FTRs (MWs) [Member] | WPL [Member]
Notional Unit Amount Of Derivatives	3,000
2012 [Member] | Natural Gas (Dths) [Member]
Notional Unit Amount Of Derivatives	41,958,000
2012 [Member] | Natural Gas (Dths) [Member] | IPL [Member]
Notional Unit Amount Of Derivatives	26,291,000
2012 [Member] | Natural Gas (Dths) [Member] | WPL [Member]
Notional Unit Amount Of Derivatives	15,667,000
2013 [Member] | Electricity (MWhs) [Member]
Notional Unit Amount Of Derivatives	3,530,000
2013 [Member] | Electricity (MWhs) [Member] | IPL [Member]
Notional Unit Amount Of Derivatives	1,725,000
2013 [Member] | Electricity (MWhs) [Member] | WPL [Member]
Notional Unit Amount Of Derivatives	1,805,000
2013 [Member] | Natural Gas (Dths) [Member]
Notional Unit Amount Of Derivatives	20,460,000
2013 [Member] | Natural Gas (Dths) [Member] | IPL [Member]
Notional Unit Amount Of Derivatives	9,237,000
2013 [Member] | Natural Gas (Dths) [Member] | WPL [Member]
Notional Unit Amount Of Derivatives	11,223,000
2014 [Member] | Electricity (MWhs) [Member]
Notional Unit Amount Of Derivatives	509,000
2014 [Member] | Electricity (MWhs) [Member] | IPL [Member]
Notional Unit Amount Of Derivatives	71,000
2014 [Member] | Electricity (MWhs) [Member] | WPL [Member]
Notional Unit Amount Of Derivatives	438,000
2014 [Member] | Natural Gas (Dths) [Member]
Notional Unit Amount Of Derivatives	4,145,000
2014 [Member] | Natural Gas (Dths) [Member] | IPL [Member]
Notional Unit Amount Of Derivatives	1,420,000
2014 [Member] | Natural Gas (Dths) [Member] | WPL [Member]
Notional Unit Amount Of Derivatives	2,725,000