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Summary Of Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2012

Regulatory Assets - At December 31, regulatory assets were comprised of the following items (in millions):



	Alliant Energy				IPL				WPL
	2012		2011		2012		2011		2012		2011
Tax-related		$770.7		$634.7		$746.2		$614.6		$24.5		$20.1
Pension and other postretirement benefits costs	549.2		514.1		279.3		264.9		269.9		249.2
Asset retirement obligations (AROs)	62.4		65.9		38.6		48.7		23.8		17.2
Derivatives	40.2		77.7		16.3		33.5		23.9		44.2
Environmental-related costs	34.9		38.9		30.3		32.2		4.6		6.7
Emission allowances	30.0		30.0		30.0		30.0		—		—
Debt redemption costs	19.8		21.8		13.6		15.1		6.2		6.7
Proposed clean air compliance projects costs	16.7		14.9		7.8		6.9		8.9		8.0
IPL’s electric transmission service costs	16.6		24.9		16.6		24.9		—		—
Proposed coal-fired base-load projects costs	14.2		21.5		10.1		15.3		4.1		6.2
Other	57.7		50.6		29.1		31.2		28.6		19.4
		$1,612.4		$1,495.0		$1,217.9		$1,117.3		$394.5		$377.7

Regulatory Liabilities

Regulatory Liabilities - At December 31, regulatory liabilities were comprised of the following items (in millions):



	Alliant Energy				IPL				WPL
	2012		2011		2012		2011		2012		2011
Cost of removal obligations		$408.7		$404.9		$268.0		$261.9		$140.7		$143.0
IPL’s tax benefit riders	355.8		349.6		355.8		349.6		—		—
Energy conservation cost recovery	55.1		29.6		10.0		4.7		45.1		24.9
IPL’s electric transmission assets sale	32.5		45.1		32.5		45.1		—		—
Commodity cost recovery	17.7		23.8		5.2		23.2		12.5		0.6
IPL’s DAEC sale	9.5		14.6		9.5		14.6		—		—
Other	36.8		42.5		20.4		22.2		16.4		20.3
		$916.1		$910.1		$701.4		$721.3		$214.7		$188.8

Schedule of Electric Plant in Service

Electric Plant In Service - Electric plant in service by functional category at December 31 was as follows (in millions):



	Alliant Energy				IPL				WPL
	2012		2011		2012		2011		2012		2011
Generation		$4,798.9		$4,100.6		$2,393.0		$2,392.3		$2,405.9		$1,708.3
Distribution	3,981.5		3,782.1		2,205.9		2,074.8		1,775.6		1,707.3
Other	290.3		282.7		216.3		216.9		74.0		65.8
		$9,070.7		$8,165.4		$4,815.2		$4,684.0		$4,255.5		$3,481.4

Schedule of Average Rates of Depreciation

The average rates of depreciation for electric, gas and other properties, consistent with current rate-making practices, were as follows:



	IPL			WPL
	2012	2011	2010	2012	2011	2010
Electric - generation	3.7%	3.5%	3.7%	3.2%	3.3%	2.9%
Electric - distribution	2.5%	2.4%	2.7%	2.9%	2.9%	2.6%
Gas	3.4%	3.5%	3.3%	2.6%	2.6%	2.2%
Other	4.5%	4.8%	4.9%	5.3%	5.2%	6.5%

Schedule of Allowance for Funds Used During Construction

The amount of AFUDC generated by equity and debt components was as follows (in millions):



	Alliant Energy						IPL						WPL
	2012		2011		2010		2012		2011		2010		2012		2011		2010
Equity		$14.1		$7.6		$11.2		$5.2		$3.5		$3.0		$8.9		$4.1		$8.2
Debt	7.8		4.4		6.8		3.2		2.3		2.5		4.6		2.1		4.3
		$21.9		$12.0		$18.0		$8.4		$5.8		$5.5		$13.5		$6.2		$12.5

Schedule of Allowance for Funds Used During Construction Recovery Rate

The AFUDC recovery rates, computed in accordance with the prescribed regulatory formula, were as follows:



	2012	2011	2010
IPL (FERC formula)	8.2%	8.5%	4.8%
WPL (PSCW formula - retail jurisdiction) (a)	8.8%	8.8%	8.8%
WPL (FERC formula - wholesale jurisdiction)	7.9%	6.2%	7.2%

(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. Consistent with the PSCW’s retail order issued in 2009, WPL accrued AFUDC on 100% of CWIP related to the Edgewater Unit 5 emission controls project and the Columbia Units 1 and 2 emission controls project in 2012, 2011 and 2010. Consistent with the PSCW’s retail rate case order issued in 2012, WPL will earn a return on 50% of the estimated CWIP related to its Columbia Units 1 and 2 emission controls project for 2013 and will accrue AFUDC on the remaining 50% in 2013.

Schedule of Emission Allowance Amortization Expenses

Amortization of emission allowances is based upon a weighted average cost for each category of vintage year utilized during the reporting period and is recorded in “Electric production fuel and energy purchases” in the Consolidated Statements of Income as follows (in millions):



	Alliant Energy			IPL			WPL
	2012	2011	2010	2012	2011	2010	2012	2011	2010
Amortization expense	$—	$13.4	$16.5	$—	$12.9	$13.1	$—	$0.5	$3.4

Schedule of Allowance for Doubtful Accounts

Allowance for doubtful accounts at December 31 was as follows (in millions):



	Alliant Energy				IPL				WPL
	2012		2011		2012		2011		2012		2011
Customer (a)		$1.3		$1.6		$—		$—		$1.3		$1.6
Other	2.7		2.6		0.7		0.9		0.5		0.3
		$4.0		$4.2		$0.7		$0.9		$1.8		$1.9


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

Riverside Energy Center [Member]

Carrying Value of Assets Purchased

As of the closing date, the carrying values of the assets purchased were as follows (in millions):



Electric plant in service		$512.7
Accumulated depreciation	(121.4		)
Current assets	4.2
Other assets	8.0
		$403.5

IPL [Member]

Regulatory Assets

Regulatory Assets - At December 31, regulatory assets were comprised of the following items (in millions):



	Alliant Energy				IPL				WPL
	2012		2011		2012		2011		2012		2011
Tax-related		$770.7		$634.7		$746.2		$614.6		$24.5		$20.1
Pension and other postretirement benefits costs	549.2		514.1		279.3		264.9		269.9		249.2
Asset retirement obligations (AROs)	62.4		65.9		38.6		48.7		23.8		17.2
Derivatives	40.2		77.7		16.3		33.5		23.9		44.2
Environmental-related costs	34.9		38.9		30.3		32.2		4.6		6.7
Emission allowances	30.0		30.0		30.0		30.0		—		—
Debt redemption costs	19.8		21.8		13.6		15.1		6.2		6.7
Proposed clean air compliance projects costs	16.7		14.9		7.8		6.9		8.9		8.0
IPL’s electric transmission service costs	16.6		24.9		16.6		24.9		—		—
Proposed coal-fired base-load projects costs	14.2		21.5		10.1		15.3		4.1		6.2
Other	57.7		50.6		29.1		31.2		28.6		19.4
		$1,612.4		$1,495.0		$1,217.9		$1,117.3		$394.5		$377.7

Regulatory Liabilities

Regulatory Liabilities - At December 31, regulatory liabilities were comprised of the following items (in millions):



	Alliant Energy				IPL				WPL
	2012		2011		2012		2011		2012		2011
Cost of removal obligations		$408.7		$404.9		$268.0		$261.9		$140.7		$143.0
IPL’s tax benefit riders	355.8		349.6		355.8		349.6		—		—
Energy conservation cost recovery	55.1		29.6		10.0		4.7		45.1		24.9
IPL’s electric transmission assets sale	32.5		45.1		32.5		45.1		—		—
Commodity cost recovery	17.7		23.8		5.2		23.2		12.5		0.6
IPL’s DAEC sale	9.5		14.6		9.5		14.6		—		—
Other	36.8		42.5		20.4		22.2		16.4		20.3
		$916.1		$910.1		$701.4		$721.3		$214.7		$188.8

Schedule of Electric Plant in Service

Electric Plant In Service - Electric plant in service by functional category at December 31 was as follows (in millions):



	Alliant Energy				IPL				WPL
	2012		2011		2012		2011		2012		2011
Generation		$4,798.9		$4,100.6		$2,393.0		$2,392.3		$2,405.9		$1,708.3
Distribution	3,981.5		3,782.1		2,205.9		2,074.8		1,775.6		1,707.3
Other	290.3		282.7		216.3		216.9		74.0		65.8
		$9,070.7		$8,165.4		$4,815.2		$4,684.0		$4,255.5		$3,481.4

Schedule of Average Rates of Depreciation

The average rates of depreciation for electric, gas and other properties, consistent with current rate-making practices, were as follows:



	IPL			WPL
	2012	2011	2010	2012	2011	2010
Electric - generation	3.7%	3.5%	3.7%	3.2%	3.3%	2.9%
Electric - distribution	2.5%	2.4%	2.7%	2.9%	2.9%	2.6%
Gas	3.4%	3.5%	3.3%	2.6%	2.6%	2.2%
Other	4.5%	4.8%	4.9%	5.3%	5.2%	6.5%

Schedule of Allowance for Funds Used During Construction

The amount of AFUDC generated by equity and debt components was as follows (in millions):



	Alliant Energy						IPL						WPL
	2012		2011		2010		2012		2011		2010		2012		2011		2010
Equity		$14.1		$7.6		$11.2		$5.2		$3.5		$3.0		$8.9		$4.1		$8.2
Debt	7.8		4.4		6.8		3.2		2.3		2.5		4.6		2.1		4.3
		$21.9		$12.0		$18.0		$8.4		$5.8		$5.5		$13.5		$6.2		$12.5

Schedule of Allowance for Funds Used During Construction Recovery Rate

The AFUDC recovery rates, computed in accordance with the prescribed regulatory formula, were as follows:



	2012	2011	2010
IPL (FERC formula)	8.2%	8.5%	4.8%
WPL (PSCW formula - retail jurisdiction) (a)	8.8%	8.8%	8.8%
WPL (FERC formula - wholesale jurisdiction)	7.9%	6.2%	7.2%

(a)

Schedule of Emission Allowance Amortization Expenses



	Alliant Energy			IPL			WPL
	2012	2011	2010	2012	2011	2010	2012	2011	2010
Amortization expense	$—	$13.4	$16.5	$—	$12.9	$13.1	$—	$0.5	$3.4

Schedule of Allowance for Doubtful Accounts

Allowance for doubtful accounts at December 31 was as follows (in millions):



	Alliant Energy				IPL				WPL
	2012		2011		2012		2011		2012		2011
Customer (a)		$1.3		$1.6		$—		$—		$1.3		$1.6
Other	2.7		2.6		0.7		0.9		0.5		0.3
		$4.0		$4.2		$0.7		$0.9		$1.8		$1.9


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

WPL [Member]

Regulatory Assets

Regulatory Assets - At December 31, regulatory assets were comprised of the following items (in millions):



	Alliant Energy				IPL				WPL
	2012		2011		2012		2011		2012		2011
Tax-related		$770.7		$634.7		$746.2		$614.6		$24.5		$20.1
Pension and other postretirement benefits costs	549.2		514.1		279.3		264.9		269.9		249.2
Asset retirement obligations (AROs)	62.4		65.9		38.6		48.7		23.8		17.2
Derivatives	40.2		77.7		16.3		33.5		23.9		44.2
Environmental-related costs	34.9		38.9		30.3		32.2		4.6		6.7
Emission allowances	30.0		30.0		30.0		30.0		—		—
Debt redemption costs	19.8		21.8		13.6		15.1		6.2		6.7
Proposed clean air compliance projects costs	16.7		14.9		7.8		6.9		8.9		8.0
IPL’s electric transmission service costs	16.6		24.9		16.6		24.9		—		—
Proposed coal-fired base-load projects costs	14.2		21.5		10.1		15.3		4.1		6.2
Other	57.7		50.6		29.1		31.2		28.6		19.4
		$1,612.4		$1,495.0		$1,217.9		$1,117.3		$394.5		$377.7

Regulatory Liabilities

Regulatory Liabilities - At December 31, regulatory liabilities were comprised of the following items (in millions):



	Alliant Energy				IPL				WPL
	2012		2011		2012		2011		2012		2011
Cost of removal obligations		$408.7		$404.9		$268.0		$261.9		$140.7		$143.0
IPL’s tax benefit riders	355.8		349.6		355.8		349.6		—		—
Energy conservation cost recovery	55.1		29.6		10.0		4.7		45.1		24.9
IPL’s electric transmission assets sale	32.5		45.1		32.5		45.1		—		—
Commodity cost recovery	17.7		23.8		5.2		23.2		12.5		0.6
IPL’s DAEC sale	9.5		14.6		9.5		14.6		—		—
Other	36.8		42.5		20.4		22.2		16.4		20.3
		$916.1		$910.1		$701.4		$721.3		$214.7		$188.8

Schedule of Electric Plant in Service

Electric Plant In Service - Electric plant in service by functional category at December 31 was as follows (in millions):



	Alliant Energy				IPL				WPL
	2012		2011		2012		2011		2012		2011
Generation		$4,798.9		$4,100.6		$2,393.0		$2,392.3		$2,405.9		$1,708.3
Distribution	3,981.5		3,782.1		2,205.9		2,074.8		1,775.6		1,707.3
Other	290.3		282.7		216.3		216.9		74.0		65.8
		$9,070.7		$8,165.4		$4,815.2		$4,684.0		$4,255.5		$3,481.4

Schedule of Average Rates of Depreciation

The average rates of depreciation for electric, gas and other properties, consistent with current rate-making practices, were as follows:



	IPL			WPL
	2012	2011	2010	2012	2011	2010
Electric - generation	3.7%	3.5%	3.7%	3.2%	3.3%	2.9%
Electric - distribution	2.5%	2.4%	2.7%	2.9%	2.9%	2.6%
Gas	3.4%	3.5%	3.3%	2.6%	2.6%	2.2%
Other	4.5%	4.8%	4.9%	5.3%	5.2%	6.5%

Schedule of Allowance for Funds Used During Construction

The amount of AFUDC generated by equity and debt components was as follows (in millions):



	Alliant Energy						IPL						WPL
	2012		2011		2010		2012		2011		2010		2012		2011		2010
Equity		$14.1		$7.6		$11.2		$5.2		$3.5		$3.0		$8.9		$4.1		$8.2
Debt	7.8		4.4		6.8		3.2		2.3		2.5		4.6		2.1		4.3
		$21.9		$12.0		$18.0		$8.4		$5.8		$5.5		$13.5		$6.2		$12.5

Schedule of Allowance for Funds Used During Construction Recovery Rate

The AFUDC recovery rates, computed in accordance with the prescribed regulatory formula, were as follows:



	2012	2011	2010
IPL (FERC formula)	8.2%	8.5%	4.8%
WPL (PSCW formula - retail jurisdiction) (a)	8.8%	8.8%	8.8%
WPL (FERC formula - wholesale jurisdiction)	7.9%	6.2%	7.2%

(a)

Schedule of Emission Allowance Amortization Expenses



	Alliant Energy			IPL			WPL
	2012	2011	2010	2012	2011	2010	2012	2011	2010
Amortization expense	$—	$13.4	$16.5	$—	$12.9	$13.1	$—	$0.5	$3.4

Schedule of Allowance for Doubtful Accounts

Allowance for doubtful accounts at December 31 was as follows (in millions):



	Alliant Energy				IPL				WPL
	2012		2011		2012		2011		2012		2011
Customer (a)		$1.3		$1.6		$—		$—		$1.3		$1.6
Other	2.7		2.6		0.7		0.9		0.5		0.3
		$4.0		$4.2		$0.7		$0.9		$1.8		$1.9


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

WPL [Member] | Riverside Energy Center [Member]

Carrying Value of Assets Purchased

As of the closing date, the carrying values of the assets purchased were as follows (in millions):



Electric plant in service		$512.7
Accumulated depreciation	(121.4		)
Current assets	4.2
Other assets	8.0
		$403.5

- Definition

Tabular disclosure of a material business combination completed during the period, including background, timing, and recognized assets and liabilities. This table does not include leveraged buyouts.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 141

-Paragraph 51

-Subparagraph a

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 141R

-Paragraph F4

-Subparagraph e

-Appendix F

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 805

-SubTopic 10

-Section 50

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=7659399&loc=d3e1392-128463

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 141R

-Paragraph 68

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 5: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 805

-SubTopic 10

-Section 50

-Paragraph 3

-URI http://asc.fasb.org/extlink&oid=7659399&loc=d3e1486-128463

Reference 6: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 141

-Paragraph 52

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

+ Details

- Definition

Tabular disclosure of assets that are created when regulatory agencies permit public utilities to defer certain costs included in rate-setting to the balance sheet.

+ References+ Details