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Summary Of Significant Accounting Policies (Tables)

6 Months Ended

Jun. 30, 2013

Regulatory Assets

Regulatory assets were comprised of the following items (in millions):

	Alliant Energy								IPL								WPL
	June 30, 2013				December 31, 2012				June 30, 2013				December 31, 2012				June 30, 2013				December 31, 2012
Tax-related		$793.1				$770.7				$768.2				$746.2				$24.9				$24.5
Pension and other postretirement benefits costs	533.2				549.2				271.7				279.3				261.5				269.9
Asset retirement obligations (AROs)	66.6				62.4				39.2				38.6				27.4				23.8
Derivatives	37.1				40.2				10.0				16.3				27.1				23.9
Environmental-related costs	31.5				34.9				27.2				30.3				4.3				4.6
Emission allowances	30.0				30.0				30.0				30.0				—				—
Other	120.6				125.0				77.9				77.2				42.7				47.8
		$1,612.1				$1,612.4				$1,224.2				$1,217.9				$387.9				$394.5

Regulatory Liabilities

Regulatory liabilities were comprised of the following items (in millions):

	Alliant Energy								IPL								WPL
	June 30, 2013				December 31, 2012				June 30, 2013				December 31, 2012				June 30, 2013				December 31, 2012
Cost of removal obligations		$412.8				$408.7				$273.1				$268.0				$139.7				$140.7
IPL’s tax benefit riders	313.0				355.8				313.0				355.8				—				—
Energy conservation cost recovery	62.1				55.1				16.7				10.0				45.4				45.1
IPL’s electric transmission assets sale	27.1				32.5				27.1				32.5				—				—
Commodity cost recovery	25.0				17.7				7.4				5.2				17.6				12.5
Other	58.1				46.3				35.1				29.9				23.0				16.4
		$898.1				$916.1				$672.4				$701.4				$225.7				$214.7

IPL [Member]

Regulatory Assets

Regulatory assets were comprised of the following items (in millions):

	Alliant Energy								IPL								WPL
	June 30, 2013				December 31, 2012				June 30, 2013				December 31, 2012				June 30, 2013				December 31, 2012
Tax-related		$793.1				$770.7				$768.2				$746.2				$24.9				$24.5
Pension and other postretirement benefits costs	533.2				549.2				271.7				279.3				261.5				269.9
Asset retirement obligations (AROs)	66.6				62.4				39.2				38.6				27.4				23.8
Derivatives	37.1				40.2				10.0				16.3				27.1				23.9
Environmental-related costs	31.5				34.9				27.2				30.3				4.3				4.6
Emission allowances	30.0				30.0				30.0				30.0				—				—
Other	120.6				125.0				77.9				77.2				42.7				47.8
		$1,612.1				$1,612.4				$1,224.2				$1,217.9				$387.9				$394.5

Regulatory Liabilities

Regulatory liabilities were comprised of the following items (in millions):

	Alliant Energy								IPL								WPL
	June 30, 2013				December 31, 2012				June 30, 2013				December 31, 2012				June 30, 2013				December 31, 2012
Cost of removal obligations		$412.8				$408.7				$273.1				$268.0				$139.7				$140.7
IPL’s tax benefit riders	313.0				355.8				313.0				355.8				—				—
Energy conservation cost recovery	62.1				55.1				16.7				10.0				45.4				45.1
IPL’s electric transmission assets sale	27.1				32.5				27.1				32.5				—				—
Commodity cost recovery	25.0				17.7				7.4				5.2				17.6				12.5
Other	58.1				46.3				35.1				29.9				23.0				16.4
		$898.1				$916.1				$672.4				$701.4				$225.7				$214.7

WPL [Member]

Regulatory Assets

Regulatory assets were comprised of the following items (in millions):

	Alliant Energy								IPL								WPL
	June 30, 2013				December 31, 2012				June 30, 2013				December 31, 2012				June 30, 2013				December 31, 2012
Tax-related		$793.1				$770.7				$768.2				$746.2				$24.9				$24.5
Pension and other postretirement benefits costs	533.2				549.2				271.7				279.3				261.5				269.9
Asset retirement obligations (AROs)	66.6				62.4				39.2				38.6				27.4				23.8
Derivatives	37.1				40.2				10.0				16.3				27.1				23.9
Environmental-related costs	31.5				34.9				27.2				30.3				4.3				4.6
Emission allowances	30.0				30.0				30.0				30.0				—				—
Other	120.6				125.0				77.9				77.2				42.7				47.8
		$1,612.1				$1,612.4				$1,224.2				$1,217.9				$387.9				$394.5

Regulatory Liabilities

Regulatory liabilities were comprised of the following items (in millions):

	Alliant Energy								IPL								WPL
	June 30, 2013				December 31, 2012				June 30, 2013				December 31, 2012				June 30, 2013				December 31, 2012
Cost of removal obligations		$412.8				$408.7				$273.1				$268.0				$139.7				$140.7
IPL’s tax benefit riders	313.0				355.8				313.0				355.8				—				—
Energy conservation cost recovery	62.1				55.1				16.7				10.0				45.4				45.1
IPL’s electric transmission assets sale	27.1				32.5				27.1				32.5				—				—
Commodity cost recovery	25.0				17.7				7.4				5.2				17.6				12.5
Other	58.1				46.3				35.1				29.9				23.0				16.4
		$898.1				$916.1				$672.4				$701.4				$225.7				$214.7

X

- 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

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 71

-Paragraph 10

-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 71

-Paragraph 9

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 980

-SubTopic 340

-Section 50

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6499975&loc=d3e44250-110382



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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 980

-SubTopic 715

-Section 50

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6501251&loc=d3e52485-110419



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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 980

-SubTopic 340

-Section 50

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=6499975&loc=d3e44264-110382

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X

- Definition

Tabular disclosure of regulatory liabilities. Detailed information about liabilities that result from rate actions of a regulator. Rate actions of a regulator can impose a liability on a regulated enterprise resulting in a regulatory liability.

+ References

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 71

-Paragraph 11

-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

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