Summary Of Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2011

Regulatory Assets

	Alliant Energy				IPL				WPL
	2011		2010		2011		2010		2011		2010
Tax-related	$	634.7	$	395.9	$	614.6	$	377.2	$	20.1	$	18.7
Pension and other postretirement benefits costs		514.1		418.9		264.9		217.4		249.2		201.5
Derivatives		77.7		66.8		33.5		24.0		44.2		42.8
Asset retirement obligations (AROs)		65.9		49.6		48.7		33.2		17.2		16.4
Environmental-related costs		38.9		38.4		32.2		32.1		6.7		6.3
Emission allowances		30.0		—		30.0		—		—		—
IPL's electric transmission service costs		24.9		33.3		24.9		33.3		—		—
Debt redemption costs		21.8		23.7		15.1		16.5		6.7		7.2
Proposed base-load projects costs		21.5		27.3		15.3		18.9		6.2		8.4
IPL's Sixth Street Generating Station (Sixth Street) costs		13.1		15.7		13.1		15.7		—		—
Proposed clean air compliance projects costs		14.9		17.9		6.9		9.5		8.0		8.4
IPL's flood-related costs		8.0		11.7		8.0		11.7		—		—
Wholesale customer rate recovery		3.6		10.5		0.9		2.6		2.7		7.9
Other		25.9		32.0		9.2		7.5		16.7		24.5
	$	1,495.0	$	1,141.7	$	1,117.3	$	799.6	$	377.7	$	342.1

Regulatory Liabilities

	Alliant Energy				IPL				WPL
	2011		2010		2011		2010		2011		2010
Cost of removal obligations	$	404.9	$	395.4	$	261.9	$	257.6	$	143.0	$	137.8
IPL's tax benefit rider		349.6		193.5		349.6		193.5		—		—
IPL's electric transmission assets sale		45.1		71.8		45.1		71.8		—		—
Energy conservation cost recovery		29.6		8.6		4.7		1.7		24.9		6.9
Commodity cost recovery		23.8		12.7		23.2		7.5		0.6		5.2
IPL's DAEC sale		14.6		42.3		14.6		42.3		—		—
Emission allowances		—		34.4		—		33.9		—		0.5
Other		42.5		41.4		22.2		19.6		20.3		21.8
	$	910.1	$	800.1	$	721.3	$	627.9	$	188.8	$	172.2

Schedule Of Cash And Cash Equivalents

	2011		2010
Total cash and cash equivalents	$	11.4	$159.3
Money market fund investments		—	$128.3
Interest rates on money market fund investments		N/A	0.17% - 0.19%

Schedule Of Electric Plant In Service

	Alliant Energy				IPL				WPL
	2011		2010		2011		2010		2011		2010
Generation	$	4,100.6	$	3,818.9	$	2,392.3	$	2,387.7	$	1,708.3	$	1,431.2
Distribution		3,782.1		3,575.6		2,074.8		1,954.1		1,707.3		1,621.5
Other		282.7		282.3		216.9		220.4		65.8		61.9
	$	8,165.4	$	7,676.8	$	4,684.0	$	4,562.2	$	3,481.4	$	3,114.6

Schedule Of Average Rates Of Depreciation

	IPL									WPL
	2011			2010			2009			2011			2010			2009
Electric:
Generation		3.5	%		3.7	%		3.4	%		3.3	%		2.9	%		3.2	%
Distribution		2.4	%		2.7	%		2.7	%		2.9	%		2.6	%		3.0	%
Gas		3.5	%		3.3	%		3.1	%		2.6	%		2.2	%		2.8	%
Other		4.8	%		4.9	%		6.0	%		5.2	%		6.5	%		6.4	%

Schedule Of Allowance For Funds Used During Construction

	Alliant Energy						IPL						WPL
	2011		2010		2009		2011		2010		2009		2011		2010		2009
Equity	$	7.6	$	11.2	$	28.2	$	3.5	$	3.0	$	24.2	$	4.1	$	8.2	$	4.0
Debt		4.4		6.8		11.5		2.3		2.5		9.8		2.1		4.3		1.7
	$	12.0	$	18.0	$	39.7	$	5.8	$	5.5	$	34.0	$	6.2	$	12.5	$	5.7

Schedule Of Allowance For Funds Used During Construction Recovery Rate

	2011			2010			2009
IPL (FERC formula - Whispering Willow - East)		N/A			N/A			8.4	%
IPL (FERC formula - other projects)		8.5	%		4.8	%		8.0	%
WPL (PSCW formula - retail jurisdiction) (a)		8.8	%		8.8	%		9.0	%
WPL (FERC formula - wholesale jurisdiction)		6.2	%		7.2	%		6.7	%

(a) Consistent with the PSCW's retail rate case order issued in 2009, WPL earned a current return on 50% of the estimated CWIP related to its Bent Tree - Phase I wind project for 2010 and accrued AFUDC on the remaining 50% in 2010. In addition, the PSCW's order changed WPL's AFUDC recovery rate to 8.8% from 9.0% effective Jan. 1, 2010.

Schedule Of Allowance For Doubtful Accounts

	Alliant Energy				IPL				WPL
	2011		2010		2011		2010		2011		2010
Customer (a)	$	1.6	$	2.5	$	—	$	—	$	1.6	$	1.4
Other		2.6		1.9		0.9		0.4		0.3		0.3
	$	4.2	$	4.4	$	0.9	$	0.4	$	1.9	$	1.7

(a) Refer to Note 4(a) for discussion of IPL's sales of accounts receivable program.

WPL's Edgewater Unit 5 Purchase [Member] | WPL [Member]

Carrying Value Of Assets Purchased

Electric plant in service	$	84
Accumulated depreciation		(50	)
CWIP		2
Production fuel		1
Materials and supplies		1
	$	38