Valuation and Qualifying Accounts And Reserves

12 Months Ended

Dec. 31, 2018

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 (c)
		Year ended December 31, 2018		$12.0		$21.2		$1.0		$23.7		$10.5
		Year ended December 31, 2017	8.7		15.1		5.4		17.2		12.0
		Year ended December 31, 2016	4.8		17.4		8.8		22.3		8.7
	IPL (c)
		Year ended December 31, 2018		$1.3		$20.9		$—		$19.1		$3.1
		Year ended December 31, 2017	1.1		14.9		—		14.7		1.3
		Year ended December 31, 2016	0.6		17.2		—		16.7		1.1
	WPL
		Year ended December 31, 2018		$10.7		$0.3		$1.0		$4.6		$7.4
		Year ended December 31, 2017	7.1		0.2		5.4		2.0		10.7
		Year ended December 31, 2016	3.7		0.1		8.8		5.5		7.1

Note: The above provisions relate to various customer, notes and other receivable balances included in various line items on the respective balance sheets.

Other Reserves:

Accumulated Provision for Other Reserves (d):
	Alliant Energy
		Year ended December 31, 2018		$23.0		$1.4		$—		$9.5		$14.9
		Year ended December 31, 2017	25.1		3.3		5.1		10.5		23.0
		Year ended December 31, 2016	27.1		6.1		—		8.1		25.1
	IPL
		Year ended December 31, 2018		$7.6		$0.9		$—		$2.1		$6.4
		Year ended December 31, 2017	8.7		0.3		—		1.4		7.6
		Year ended December 31, 2016	9.4		1.0		—		1.7		8.7
	WPL
		Year ended December 31, 2018		$6.4		$0.5		$—		$2.3		$4.6
		Year ended December 31, 2017	8.1		0.1		—		1.8		6.4
		Year ended December 31, 2016	11.4		1.8		—		5.1		8.1

(a) Accumulated provision for uncollectible accounts: In accordance with its regulatory treatment, certain amounts provided by WPL are recorded in regulatory assets. WPL expenses these amounts when an uncollectible account is written-off.

Accumulated provision for other reserves: In 2017, Alliant Energy recorded amounts to deferred tax liabilities related to the impacts of Federal Tax Reform.

(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 5(b) 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, and the impacts of Federal Tax Reform.

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 (c)
		Year ended December 31, 2018		$12.0		$21.2		$1.0		$23.7		$10.5
		Year ended December 31, 2017	8.7		15.1		5.4		17.2		12.0
		Year ended December 31, 2016	4.8		17.4		8.8		22.3		8.7
	IPL (c)
		Year ended December 31, 2018		$1.3		$20.9		$—		$19.1		$3.1
		Year ended December 31, 2017	1.1		14.9		—		14.7		1.3
		Year ended December 31, 2016	0.6		17.2		—		16.7		1.1
	WPL
		Year ended December 31, 2018		$10.7		$0.3		$1.0		$4.6		$7.4
		Year ended December 31, 2017	7.1		0.2		5.4		2.0		10.7
		Year ended December 31, 2016	3.7		0.1		8.8		5.5		7.1

Note: The above provisions relate to various customer, notes and other receivable balances included in various line items on the respective balance sheets.

Other Reserves:

Accumulated Provision for Other Reserves (d):
	Alliant Energy
		Year ended December 31, 2018		$23.0		$1.4		$—		$9.5		$14.9
		Year ended December 31, 2017	25.1		3.3		5.1		10.5		23.0
		Year ended December 31, 2016	27.1		6.1		—		8.1		25.1
	IPL
		Year ended December 31, 2018		$7.6		$0.9		$—		$2.1		$6.4
		Year ended December 31, 2017	8.7		0.3		—		1.4		7.6
		Year ended December 31, 2016	9.4		1.0		—		1.7		8.7
	WPL
		Year ended December 31, 2018		$6.4		$0.5		$—		$2.3		$4.6
		Year ended December 31, 2017	8.1		0.1		—		1.8		6.4
		Year ended December 31, 2016	11.4		1.8		—		5.1		8.1

(a) Accumulated provision for uncollectible accounts: In accordance with its regulatory treatment, certain amounts provided by WPL are recorded in regulatory assets. WPL expenses these amounts when an uncollectible account is written-off.

Accumulated provision for other reserves: In 2017, Alliant Energy recorded amounts to deferred tax liabilities related to the impacts of Federal Tax Reform.

(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 5(b) 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, and the impacts of Federal Tax Reform.

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 (c)
		Year ended December 31, 2018		$12.0		$21.2		$1.0		$23.7		$10.5
		Year ended December 31, 2017	8.7		15.1		5.4		17.2		12.0
		Year ended December 31, 2016	4.8		17.4		8.8		22.3		8.7
	IPL (c)
		Year ended December 31, 2018		$1.3		$20.9		$—		$19.1		$3.1
		Year ended December 31, 2017	1.1		14.9		—		14.7		1.3
		Year ended December 31, 2016	0.6		17.2		—		16.7		1.1
	WPL
		Year ended December 31, 2018		$10.7		$0.3		$1.0		$4.6		$7.4
		Year ended December 31, 2017	7.1		0.2		5.4		2.0		10.7
		Year ended December 31, 2016	3.7		0.1		8.8		5.5		7.1

Note: The above provisions relate to various customer, notes and other receivable balances included in various line items on the respective balance sheets.

Other Reserves:

Accumulated Provision for Other Reserves (d):
	Alliant Energy
		Year ended December 31, 2018		$23.0		$1.4		$—		$9.5		$14.9
		Year ended December 31, 2017	25.1		3.3		5.1		10.5		23.0
		Year ended December 31, 2016	27.1		6.1		—		8.1		25.1
	IPL
		Year ended December 31, 2018		$7.6		$0.9		$—		$2.1		$6.4
		Year ended December 31, 2017	8.7		0.3		—		1.4		7.6
		Year ended December 31, 2016	9.4		1.0		—		1.7		8.7
	WPL
		Year ended December 31, 2018		$6.4		$0.5		$—		$2.3		$4.6
		Year ended December 31, 2017	8.1		0.1		—		1.8		6.4
		Year ended December 31, 2016	11.4		1.8		—		5.1		8.1

(a) Accumulated provision for uncollectible accounts: In accordance with its regulatory treatment, certain amounts provided by WPL are recorded in regulatory assets. WPL expenses these amounts when an uncollectible account is written-off.

Accumulated provision for other reserves: In 2017, Alliant Energy recorded amounts to deferred tax liabilities related to the impacts of Federal Tax Reform.

(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 5(b) 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, and the impacts of Federal Tax Reform.