Summary Of Significant Accounting Policies (Tables)

9 Months Ended

Sep. 30, 2012

Accounting Policies [Abstract]

Regulatory Assets

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

	Alliant Energy				IPL				WPL
	September 30, 2012		December 31, 2011		September 30, 2012		December 31, 2011		September 30, 2012		December 31, 2011
Tax-related		$709.4		$634.7		$686.2		$614.6		$23.2		$20.1
Pension and other postretirement benefits costs	495.4		514.1		256.3		264.9		239.1		249.2
Asset retirement obligations (AROs)	57.8		65.9		38.7		48.7		19.1		17.2
Derivatives	56.6		77.7		22.6		33.5		34.0		44.2
Environmental-related costs	36.3		38.9		31.5		32.2		4.8		6.7
Emission allowances	30.0		30.0		30.0		30.0		—		—
Debt redemption costs	20.3		21.8		14.0		15.1		6.3		6.7
IPL’s electric transmission service costs	18.7		24.9		18.7		24.9		—		—
Proposed base-load projects costs	16.0		21.5		11.4		15.3		4.6		6.2
Other	77.9		65.5		41.6		38.1		36.3		27.4
		$1,518.4		$1,495.0		$1,151.0		$1,117.3		$367.4		$377.7

Regulatory Liabilities

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

	Alliant Energy				IPL				WPL
	September 30, 2012		December 31, 2011		September 30, 2012		December 31, 2011		September 30, 2012		December 31, 2011
Cost of removal obligations		$406.6		$404.9		$266.5		$261.9		$140.1		$143.0
IPL’s tax benefit rider	327.4		349.6		327.4		349.6		—		—
Energy conservation cost recovery	48.8		29.6		8.9		4.7		39.9		24.9
IPL’s electric transmission assets sale	35.2		45.1		35.2		45.1		—		—
Derivatives	21.3		7.2		10.2		3.6		11.1		3.6
Commodity cost recovery	20.4		23.8		14.8		23.2		5.6		0.6
Other	46.7		49.9		25.1		33.2		21.6		16.7
		$906.4		$910.1		$688.1		$721.3		$218.3		$188.8