Valuation and Qualifying Accounts And Reserves

12 Months Ended

Dec. 31, 2012

Valuation and Qualifying Accounts Disclosure [Line Items]

Valuation and Qualifying Accounts And Reserves

SCHEDULE II - VALUATION AND QUALIFYING ACCOUNTS AND RESERVES

		Additions
	Balance,	Charged to	Charged to Other		Balance,
Description	January 1	Expense	Accounts (a)	Deductions (b)	December 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 (c)
		Year ended December 31, 2012		$4.2		$6.6		$1.2		$8.0		$4.0
		Year ended December 31, 2011	3.2		7.8		1.9		8.7		4.2
		Year ended December 31, 2010	4.5		6.8		1.8		9.9		3.2
	Interstate Power and Light Company (c)
		Year ended December 31, 2012		$0.9		$6.4		$—		$6.6		$0.7
		Year ended December 31, 2011	0.4		7.4		—		6.9		0.9
		Year ended December 31, 2010	2.5		5.6		—		7.7		0.4
	Wisconsin Power and Light Company
		Year ended December 31, 2012		$1.9		$0.1		$1.2		$1.4		$1.8
		Year ended December 31, 2011	1.7		0.1		1.9		1.8		1.9
		Year ended December 31, 2010	2.0		0.1		1.8		2.2		1.7

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 December 31, 2012		$25.9		$9.6		$—		$2.1		$33.4
		Year ended December 31, 2011	24.0		8.8		—		6.9		25.9
		Year ended December 31, 2010	20.9		11.5		—		8.4		24.0
	Interstate Power and Light Company
		Year ended December 31, 2012		$10.2		$2.1		$—		$0.7		$11.6
		Year ended December 31, 2011	8.8		3.6		—		2.2		10.2
		Year ended December 31, 2010	9.0		2.0		—		2.2		8.8
	Wisconsin Power and Light Company
		Year ended December 31, 2012		$11.7		$3.1		$—		$1.3		$13.5
		Year ended December 31, 2011	12.8		3.7		—		4.8		11.7
		Year ended December 31, 2010	10.7		7.5		—		5.4		12.8

(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.

IPL [Member]

Valuation and Qualifying Accounts Disclosure [Line Items]

Valuation and Qualifying Accounts And Reserves

SCHEDULE II - VALUATION AND QUALIFYING ACCOUNTS AND RESERVES

		Additions
	Balance,	Charged to	Charged to Other		Balance,
Description	January 1	Expense	Accounts (a)	Deductions (b)	December 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 (c)
		Year ended December 31, 2012		$4.2		$6.6		$1.2		$8.0		$4.0
		Year ended December 31, 2011	3.2		7.8		1.9		8.7		4.2
		Year ended December 31, 2010	4.5		6.8		1.8		9.9		3.2
	Interstate Power and Light Company (c)
		Year ended December 31, 2012		$0.9		$6.4		$—		$6.6		$0.7
		Year ended December 31, 2011	0.4		7.4		—		6.9		0.9
		Year ended December 31, 2010	2.5		5.6		—		7.7		0.4
	Wisconsin Power and Light Company
		Year ended December 31, 2012		$1.9		$0.1		$1.2		$1.4		$1.8
		Year ended December 31, 2011	1.7		0.1		1.9		1.8		1.9
		Year ended December 31, 2010	2.0		0.1		1.8		2.2		1.7

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 December 31, 2012		$25.9		$9.6		$—		$2.1		$33.4
		Year ended December 31, 2011	24.0		8.8		—		6.9		25.9
		Year ended December 31, 2010	20.9		11.5		—		8.4		24.0
	Interstate Power and Light Company
		Year ended December 31, 2012		$10.2		$2.1		$—		$0.7		$11.6
		Year ended December 31, 2011	8.8		3.6		—		2.2		10.2
		Year ended December 31, 2010	9.0		2.0		—		2.2		8.8
	Wisconsin Power and Light Company
		Year ended December 31, 2012		$11.7		$3.1		$—		$1.3		$13.5
		Year ended December 31, 2011	12.8		3.7		—		4.8		11.7
		Year ended December 31, 2010	10.7		7.5		—		5.4		12.8

(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.

WPL [Member]

Valuation and Qualifying Accounts Disclosure [Line Items]

Valuation and Qualifying Accounts And Reserves

SCHEDULE II - VALUATION AND QUALIFYING ACCOUNTS AND RESERVES

		Additions
	Balance,	Charged to	Charged to Other		Balance,
Description	January 1	Expense	Accounts (a)	Deductions (b)	December 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 (c)
		Year ended December 31, 2012		$4.2		$6.6		$1.2		$8.0		$4.0
		Year ended December 31, 2011	3.2		7.8		1.9		8.7		4.2
		Year ended December 31, 2010	4.5		6.8		1.8		9.9		3.2
	Interstate Power and Light Company (c)
		Year ended December 31, 2012		$0.9		$6.4		$—		$6.6		$0.7
		Year ended December 31, 2011	0.4		7.4		—		6.9		0.9
		Year ended December 31, 2010	2.5		5.6		—		7.7		0.4
	Wisconsin Power and Light Company
		Year ended December 31, 2012		$1.9		$0.1		$1.2		$1.4		$1.8
		Year ended December 31, 2011	1.7		0.1		1.9		1.8		1.9
		Year ended December 31, 2010	2.0		0.1		1.8		2.2		1.7

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 December 31, 2012		$25.9		$9.6		$—		$2.1		$33.4
		Year ended December 31, 2011	24.0		8.8		—		6.9		25.9
		Year ended December 31, 2010	20.9		11.5		—		8.4		24.0
	Interstate Power and Light Company
		Year ended December 31, 2012		$10.2		$2.1		$—		$0.7		$11.6
		Year ended December 31, 2011	8.8		3.6		—		2.2		10.2
		Year ended December 31, 2010	9.0		2.0		—		2.2		8.8
	Wisconsin Power and Light Company
		Year ended December 31, 2012		$11.7		$3.1		$—		$1.3		$13.5
		Year ended December 31, 2011	12.8		3.7		—		4.8		11.7
		Year ended December 31, 2010	10.7		7.5		—		5.4		12.8

(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.