Valuation And Qualifying Accounts And Reserves

12 Months Ended

Dec. 31, 2011

Valuation And Qualifying Accounts And Reserves [Abstract]

Valuation And Qualifying Accounts And Reserves

SCHEDULE II - VALUATION AND QUALIFYING ACCOUNTS AND RESERVES

		$11.0		$11.0		$11.0		$11.0		$11.0
			Additions
Description	Balance, Jan. 1		Charged to Expense		Charged to Other Accounts (a)		Deductions (b)		Balance, Dec. 31
	(in millions)
Valuation and Qualifying Accounts Which are Deducted in the Balance Sheet From the Assets to Which They Apply:
Accumulated Provision for Uncollectible Accounts:
Alliant Energy Corporation
Year ended Dec. 31, 2011 (c)	$	4.4	$	7.7	$	1.9	$	9.8	$	4.2
Year ended Dec. 31, 2010 (c)		5.5		7.7		1.8		10.6		4.4
Year ended Dec. 31, 2009		6.6		8.9		2.4		12.4		5.5
Interstate Power and Light Company
Year ended Dec. 31, 2011 (c)	$	0.4	$	7.4	$	—	$	6.9	$	0.9
Year ended Dec. 31, 2010 (c)		2.5		5.6		—		7.7		0.4
Year ended Dec. 31, 2009		4.2		8.2		—		9.9		2.5
Wisconsin Power and Light Company
Year ended Dec. 31, 2011	$	1.7	$	0.1	$	1.9	$	1.8	$	1.9
Year ended Dec. 31, 2010		2.0		0.1		1.8		2.2		1.7
Year ended Dec. 31, 2009		1.8		0.1		2.4		2.3		2.0
Note: The above provisions relate to various customer, notes and other receivable balances included in various line items on the respective Consolidated Balance Sheets.
Other Reserves:
Accumulated Provision for Other Reserves (d):
Alliant Energy Corporation
Year ended Dec. 31, 2011	$	25.7	$	20.3	$	—	$	11.0	$	35.0
Year ended Dec. 31, 2010		22.9		14.5		—		11.7		25.7
Year ended Dec. 31, 2009		17.9		12.6		—		7.6		22.9
Interstate Power and Light Company
Year ended Dec. 31, 2011	$	8.8	$	3.6	$	—	$	2.2	$	10.2
Year ended Dec. 31, 2010		9.0		2.0		—		2.2		8.8
Year ended Dec. 31, 2009		7.1		3.6		—		1.7		9.0
Wisconsin Power and Light Company
Year ended Dec. 31, 2011	$	12.8	$	3.7	$	—	$	4.8	$	11.7
Year ended Dec. 31, 2010		10.7		7.5		—		5.4		12.8
Year ended Dec. 31, 2009		7.1		6.5		—		2.9		10.7

(a) Accumulated provision for uncollectible accounts: In accordance with its regulatory treatment, certain amounts provided by Wisconsin Power and Light Company are recorded in regulatory assets.

(b) Deductions are of the nature for which the reserves were created. In the case of the accumulated provision for uncollectible accounts, deductions from this reserve are reduced by recoveries of amounts previously written off.

(c) Refer to Note 4(a) of the "Combined Notes to Consolidated Financial Statements" for discussion of IPL's sales of accounts receivable program.

(d) Other reserves are largely related to injury and damage claims arising in the ordinary course of business.