Derivative Instruments (Notional Amounts Of Derivative Instruments) (Details) (Commodity [Member])	Jun. 30, 2012 MWh
Electricity (MWhs) [Member] | Alliant Energy [Member]
Notional Amount of Derivatives [Line Items]
Notional Unit Amount Of Derivatives (in MWhs/MWs/Dths)	6,887,000
Electricity (MWhs) [Member] | IPL [Member]
Notional Amount of Derivatives [Line Items]
Notional Unit Amount Of Derivatives (in MWhs/MWs/Dths)	3,518,000
Electricity (MWhs) [Member] | WPL [Member]
Notional Amount of Derivatives [Line Items]
Notional Unit Amount Of Derivatives (in MWhs/MWs/Dths)	3,369,000
FTRs (MWs) [Member] | Alliant Energy [Member]
Notional Amount of Derivatives [Line Items]
Notional Unit Amount Of Derivatives (in MWhs/MWs/Dths)	59,000
FTRs (MWs) [Member] | IPL [Member]
Notional Amount of Derivatives [Line Items]
Notional Unit Amount Of Derivatives (in MWhs/MWs/Dths)	32,000
FTRs (MWs) [Member] | WPL [Member]
Notional Amount of Derivatives [Line Items]
Notional Unit Amount Of Derivatives (in MWhs/MWs/Dths)	27,000
Natural Gas (Dths) [Member] | Alliant Energy [Member]
Notional Amount of Derivatives [Line Items]
Notional Unit Amount Of Derivatives (in MWhs/MWs/Dths)	59,570,000
Natural Gas (Dths) [Member] | IPL [Member]
Notional Amount of Derivatives [Line Items]
Notional Unit Amount Of Derivatives (in MWhs/MWs/Dths)	35,665,000
Natural Gas (Dths) [Member] | WPL [Member]
Notional Amount of Derivatives [Line Items]
Notional Unit Amount Of Derivatives (in MWhs/MWs/Dths)	23,905,000
2012 [Member] | Electricity (MWhs) [Member] | Alliant Energy [Member]
Notional Amount of Derivatives [Line Items]
Notional Unit Amount Of Derivatives (in MWhs/MWs/Dths)	2,726,000
2012 [Member] | Electricity (MWhs) [Member] | IPL [Member]
Notional Amount of Derivatives [Line Items]
Notional Unit Amount Of Derivatives (in MWhs/MWs/Dths)	1,600,000
2012 [Member] | Electricity (MWhs) [Member] | WPL [Member]
Notional Amount of Derivatives [Line Items]
Notional Unit Amount Of Derivatives (in MWhs/MWs/Dths)	1,126,000
2012 [Member] | FTRs (MWs) [Member] | Alliant Energy [Member]
Notional Amount of Derivatives [Line Items]
Notional Unit Amount Of Derivatives (in MWhs/MWs/Dths)	31,000
2012 [Member] | FTRs (MWs) [Member] | IPL [Member]
Notional Amount of Derivatives [Line Items]
Notional Unit Amount Of Derivatives (in MWhs/MWs/Dths)	17,000
2012 [Member] | FTRs (MWs) [Member] | WPL [Member]
Notional Amount of Derivatives [Line Items]
Notional Unit Amount Of Derivatives (in MWhs/MWs/Dths)	14,000
2012 [Member] | Natural Gas (Dths) [Member] | Alliant Energy [Member]
Notional Amount of Derivatives [Line Items]
Notional Unit Amount Of Derivatives (in MWhs/MWs/Dths)	33,281,000
2012 [Member] | Natural Gas (Dths) [Member] | IPL [Member]
Notional Amount of Derivatives [Line Items]
Notional Unit Amount Of Derivatives (in MWhs/MWs/Dths)	22,703,000
2012 [Member] | Natural Gas (Dths) [Member] | WPL [Member]
Notional Amount of Derivatives [Line Items]
Notional Unit Amount Of Derivatives (in MWhs/MWs/Dths)	10,578,000
2013 [Member] | Electricity (MWhs) [Member] | Alliant Energy [Member]
Notional Amount of Derivatives [Line Items]
Notional Unit Amount Of Derivatives (in MWhs/MWs/Dths)	3,652,000
2013 [Member] | Electricity (MWhs) [Member] | IPL [Member]
Notional Amount of Derivatives [Line Items]
Notional Unit Amount Of Derivatives (in MWhs/MWs/Dths)	1,847,000
2013 [Member] | Electricity (MWhs) [Member] | WPL [Member]
Notional Amount of Derivatives [Line Items]
Notional Unit Amount Of Derivatives (in MWhs/MWs/Dths)	1,805,000
2013 [Member] | FTRs (MWs) [Member] | Alliant Energy [Member]
Notional Amount of Derivatives [Line Items]
Notional Unit Amount Of Derivatives (in MWhs/MWs/Dths)	28,000
2013 [Member] | FTRs (MWs) [Member] | IPL [Member]
Notional Amount of Derivatives [Line Items]
Notional Unit Amount Of Derivatives (in MWhs/MWs/Dths)	15,000
2013 [Member] | FTRs (MWs) [Member] | WPL [Member]
Notional Amount of Derivatives [Line Items]
Notional Unit Amount Of Derivatives (in MWhs/MWs/Dths)	13,000
2013 [Member] | Natural Gas (Dths) [Member] | Alliant Energy [Member]
Notional Amount of Derivatives [Line Items]
Notional Unit Amount Of Derivatives (in MWhs/MWs/Dths)	21,089,000
2013 [Member] | Natural Gas (Dths) [Member] | IPL [Member]
Notional Amount of Derivatives [Line Items]
Notional Unit Amount Of Derivatives (in MWhs/MWs/Dths)	10,937,000
2013 [Member] | Natural Gas (Dths) [Member] | WPL [Member]
Notional Amount of Derivatives [Line Items]
Notional Unit Amount Of Derivatives (in MWhs/MWs/Dths)	10,152,000
2014 [Member] | Electricity (MWhs) [Member] | Alliant Energy [Member]
Notional Amount of Derivatives [Line Items]
Notional Unit Amount Of Derivatives (in MWhs/MWs/Dths)	509,000
2014 [Member] | Electricity (MWhs) [Member] | IPL [Member]
Notional Amount of Derivatives [Line Items]
Notional Unit Amount Of Derivatives (in MWhs/MWs/Dths)	71,000
2014 [Member] | Electricity (MWhs) [Member] | WPL [Member]
Notional Amount of Derivatives [Line Items]
Notional Unit Amount Of Derivatives (in MWhs/MWs/Dths)	438,000
2014 [Member] | FTRs (MWs) [Member] | Alliant Energy [Member]
Notional Amount of Derivatives [Line Items]
Notional Unit Amount Of Derivatives (in MWhs/MWs/Dths)	0
2014 [Member] | FTRs (MWs) [Member] | IPL [Member]
Notional Amount of Derivatives [Line Items]
Notional Unit Amount Of Derivatives (in MWhs/MWs/Dths)	0
2014 [Member] | FTRs (MWs) [Member] | WPL [Member]
Notional Amount of Derivatives [Line Items]
Notional Unit Amount Of Derivatives (in MWhs/MWs/Dths)	0
2014 [Member] | Natural Gas (Dths) [Member] | Alliant Energy [Member]
Notional Amount of Derivatives [Line Items]
Notional Unit Amount Of Derivatives (in MWhs/MWs/Dths)	5,200,000
2014 [Member] | Natural Gas (Dths) [Member] | IPL [Member]
Notional Amount of Derivatives [Line Items]
Notional Unit Amount Of Derivatives (in MWhs/MWs/Dths)	2,025,000
2014 [Member] | Natural Gas (Dths) [Member] | WPL [Member]
Notional Amount of Derivatives [Line Items]
Notional Unit Amount Of Derivatives (in MWhs/MWs/Dths)	3,175,000