Derivative Instruments (Tables)

3 Months Ended

Mar. 31, 2012

Derivative Instruments [Abstract]

Notional Amounts Of Derivative Instruments

	2012		2013		2014		Total
Alliant Energy
Electricity (megawatt-hours (MWhs))		3,994		3,530		509		8,033
FTRs (MWs)		8		—		—		8
Natural gas (dekatherms (Dths))		41,958		20,460		4,145		66,563
IPL
Electricity (MWhs)		2,416		1,725		71		4,212
FTRs (MWs)		5		—		—		5
Natural gas (Dths)		26,291		9,237		1,420		36,948
WPL
Electricity (MWhs)		1,578		1,805		438		3,821
FTRs (MWs)		3		—		—		3
Natural gas (Dths)		15,667		11,223		2,725		29,615

Fair Value Of Financial Instruments

	Alliant Energy				IPL				WPL
	March 31,		Dec. 31,		March 31,		Dec. 31,		March 31,		Dec. 31,
Commodity contracts	2012		2011		2012		2011		2012		2011
Current derivative assets	$	5.6	$	12.7	$	3.9	$	9.2	$	1.7	$	3.5
Non-current derivative assets		4.8		3.0		2.0		1.4		2.8		1.6
Current derivative liabilities		61.9		55.9		30.1		24.5		31.8		31.4
Non-current derivative liabilities		21.3		22.1		8.0		9.1		13.3		13.0

Gains And Losses From Derivative Instruments Not Designated As Hedging Instruments

	Gains (Losses)
Location Recorded	Alliant Energy						IPL						WPL
on Balance Sheets	2012			2011			2012			2011			2012			2011
Regulatory assets	($	39.7	)	($	4.0	)	($	22.2	)	($	2.4	)	($	17.5	)	($	1.6	)
Regulatory liabilities		1.4			1.5			—			0.8			1.4			0.7