Summary Of Significant Accounting Policies (Tables)

6 Months Ended

Jun. 30, 2012

Accounting Policies [Abstract]

Regulatory Assets

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

	Alliant Energy				IPL				WPL
	June 30, 2012		December 31, 2011		June 30, 2012		December 31, 2011		June 30, 2012		December 31, 2011
Tax-related		$652.8		$634.7		$630.8		$614.6		$22.0		$20.1
Pension and other postretirement benefits costs	502.8		514.1		260.0		264.9		242.8		249.2
Derivatives	64.2		77.7		28.8		33.5		35.4		44.2
Asset retirement obligations	58.0		65.9		39.6		48.7		18.4		17.2
Environmental-related costs	37.1		38.9		32.2		32.2		4.9		6.7
Emission allowances	30.0		30.0		30.0		30.0		—		—
IPL’s electric transmission service costs	20.8		24.9		20.8		24.9		—		—
Debt redemption costs	20.8		21.8		14.3		15.1		6.5		6.7
Proposed base-load projects costs	17.8		21.5		12.7		15.3		5.1		6.2
Other	75.2		65.5		41.2		38.1		34.0		27.4
		$1,479.5		$1,495.0		$1,110.4		$1,117.3		$369.1		$377.7

Regulatory Liabilities

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

	Alliant Energy				IPL				WPL
	June 30, 2012		December 31, 2011		June 30, 2012		December 31, 2011		June 30, 2012		December 31, 2011
Cost of removal obligations		$406.8		$404.9		$265.0		$261.9		$141.8		$143.0
IPL’s tax benefit rider	309.1		349.6		309.1		349.6		—		—
Energy conservation cost recovery	43.5		29.6		7.8		4.7		35.7		24.9
IPL’s electric transmission assets sale	38.0		45.1		38.0		45.1		—		—
Commodity cost recovery	5.4		23.8		0.5		23.2		4.9		0.6
Other	58.8		57.1		35.5		36.8		23.3		20.3
		$861.6		$910.1		$655.9		$721.3		$205.7		$188.8