Summary Of Significant Accounting Policies (Tables)

9 Months Ended

Sep. 30, 2013

Regulatory Assets

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

	Alliant Energy				IPL				WPL
	September 30, 2013		December 31, 2012		September 30, 2013		December 31, 2012		September 30, 2013		December 31, 2012
Tax-related		$813.6		$770.7		$783.6		$746.2		$30.0		$24.5
Pension and other postretirement benefits costs	525.2		549.2		267.9		279.3		257.3		269.9
AROs	66.9		62.4		38.8		38.6		28.1		23.8
Emission allowances	30.0		30.0		30.0		30.0		—		—
Derivatives	26.8		40.2		6.9		16.3		19.9		23.9
Environmental-related costs	26.0		34.9		21.8		30.3		4.2		4.6
Other	107.7		125.0		67.0		77.2		40.7		47.8
		$1,596.2		$1,612.4		$1,216.0		$1,217.9		$380.2		$394.5

Regulatory Liabilities

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

	Alliant Energy				IPL				WPL
	September 30, 2013		December 31, 2012		September 30, 2013		December 31, 2012		September 30, 2013		December 31, 2012
Cost of removal obligations		$415.7		$408.7		$275.8		$268.0		$139.9		$140.7
IPL’s tax benefit riders	288.8		355.8		288.8		355.8		—		—
Energy conservation cost recovery	58.1		55.1		12.6		10.0		45.5		45.1
IPL’s electric transmission assets sale	24.3		32.5		24.3		32.5		—		—
Commodity cost recovery	7.0		17.7		1.1		5.2		5.9		12.5
Other	43.7		46.3		27.8		29.9		15.9		16.4
		$837.6		$916.1		$630.4		$701.4		$207.2		$214.7

IPL [Member]

Regulatory Assets

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

	Alliant Energy				IPL				WPL
	September 30, 2013		December 31, 2012		September 30, 2013		December 31, 2012		September 30, 2013		December 31, 2012
Tax-related		$813.6		$770.7		$783.6		$746.2		$30.0		$24.5
Pension and other postretirement benefits costs	525.2		549.2		267.9		279.3		257.3		269.9
AROs	66.9		62.4		38.8		38.6		28.1		23.8
Emission allowances	30.0		30.0		30.0		30.0		—		—
Derivatives	26.8		40.2		6.9		16.3		19.9		23.9
Environmental-related costs	26.0		34.9		21.8		30.3		4.2		4.6
Other	107.7		125.0		67.0		77.2		40.7		47.8
		$1,596.2		$1,612.4		$1,216.0		$1,217.9		$380.2		$394.5

Regulatory Liabilities

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

	Alliant Energy				IPL				WPL
	September 30, 2013		December 31, 2012		September 30, 2013		December 31, 2012		September 30, 2013		December 31, 2012
Cost of removal obligations		$415.7		$408.7		$275.8		$268.0		$139.9		$140.7
IPL’s tax benefit riders	288.8		355.8		288.8		355.8		—		—
Energy conservation cost recovery	58.1		55.1		12.6		10.0		45.5		45.1
IPL’s electric transmission assets sale	24.3		32.5		24.3		32.5		—		—
Commodity cost recovery	7.0		17.7		1.1		5.2		5.9		12.5
Other	43.7		46.3		27.8		29.9		15.9		16.4
		$837.6		$916.1		$630.4		$701.4		$207.2		$214.7

WPL [Member]

Regulatory Assets

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

	Alliant Energy				IPL				WPL
	September 30, 2013		December 31, 2012		September 30, 2013		December 31, 2012		September 30, 2013		December 31, 2012
Tax-related		$813.6		$770.7		$783.6		$746.2		$30.0		$24.5
Pension and other postretirement benefits costs	525.2		549.2		267.9		279.3		257.3		269.9
AROs	66.9		62.4		38.8		38.6		28.1		23.8
Emission allowances	30.0		30.0		30.0		30.0		—		—
Derivatives	26.8		40.2		6.9		16.3		19.9		23.9
Environmental-related costs	26.0		34.9		21.8		30.3		4.2		4.6
Other	107.7		125.0		67.0		77.2		40.7		47.8
		$1,596.2		$1,612.4		$1,216.0		$1,217.9		$380.2		$394.5

Regulatory Liabilities

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

	Alliant Energy				IPL				WPL
	September 30, 2013		December 31, 2012		September 30, 2013		December 31, 2012		September 30, 2013		December 31, 2012
Cost of removal obligations		$415.7		$408.7		$275.8		$268.0		$139.9		$140.7
IPL’s tax benefit riders	288.8		355.8		288.8		355.8		—		—
Energy conservation cost recovery	58.1		55.1		12.6		10.0		45.5		45.1
IPL’s electric transmission assets sale	24.3		32.5		24.3		32.5		—		—
Commodity cost recovery	7.0		17.7		1.1		5.2		5.9		12.5
Other	43.7		46.3		27.8		29.9		15.9		16.4
		$837.6		$916.1		$630.4		$701.4		$207.2		$214.7