Debt (Tables)

12 Months Ended

Dec. 31, 2011

Debt [Abstract]

Credit Facilities

	Alliant Energy						IPL					WPL
	2011			2010			2011			2010		2011			2010
Commercial paper at Dec. 31:
Amount outstanding	$	102.8		$	47.4		$	7.1		$	—	$	25.7		$	47.4
Weighted average interest rates		0.3	%		0.3	%		0.4	%		N/A		0.3	%		0.3	%

Other Short-Term Borrowings

Total short-term debt outstanding for the year ended:
Maximum amount outstanding (based on daily outstanding balances)	$	124.4		$	350.3		$	54.4		$	219.1		$	96.5		$	170.2
Average amount outstanding (based on daily outstanding balances)	$	27.7		$	92.0		$	6.0		$	62.8		$	17.6		$	36.6
Weighted average interest rates		0.3	%		0.3	%		0.3	%		0.3	%		0.3	%		0.3	%

Schedule Of Debt-To-Capital Ratios

	Alliant Energy			IPL			WPL
Requirement		Less than 65	%		Less than 58	%		Less than 58	%
Status at Dec. 31, 2011		46%			46%			45%

Schedule Of Long-Term Debt Instruments

	2011									2010
	Alliant Energy			IPL			WPL			Alliant Energy			IPL			WPL
Senior Debentures:
3.3%, due 2015	$	150.0		$	150.0		$	—		$	150.0		$	150.0		$	—
5.875%, due 2018		100.0			100.0			—			100.0			100.0			—
7.25%, due 2018		250.0			250.0			—			250.0			250.0			—
3.65%, due 2020		200.0			200.0			—			200.0			200.0			—
5.5%, due 2025		50.0			50.0			—			50.0			50.0			—
6.45%, due 2033		100.0			100.0			—			100.0			100.0			—
6.3%, due 2034		125.0			125.0			—			125.0			125.0			—
6.25%, due 2039		300.0			300.0			—			300.0			300.0			—
		1,275.0			1,275.0			—			1,275.0			1,275.0			—
Debentures:
5%, due 2019		250.0			—			250.0			250.0			—			250.0
4.6%, due 2020		150.0			—			150.0			150.0			—			150.0
6.25%, due 2034		100.0			—			100.0			100.0			—			100.0
6.375%, due 2037		300.0			—			300.0			300.0			—			300.0
7.6%, due 2038		250.0			—			250.0			250.0			—			250.0
		1,050.0			—			1,050.0			1,050.0			—			1,050.0
Pollution Control Revenue Bonds:
5%, due 2014		38.4			38.4			—			38.4			38.4			—
5%, due 2014 and 2015		24.5			—			24.5			24.5			—			24.5
5.375%, due 2015		14.6			—			14.6			14.6			—			14.6
		77.5			38.4			39.1			77.5			38.4			39.1
Other:
4% senior notes, due 2014		250.0			—			—			250.0			—			—
5.06% senior secured notes, due 2012 to 2024		63.3			—			—			64.5			—			—
Other, 1% at Dec. 31, 2011, due 2012 to 2025		0.5			—			—			0.5			—			—
		313.8			—			—			315.0			—			—
Subtotal		2,716.3			1,313.4			1,089.1			2,717.5			1,313.4			1,089.1
Current maturities		(1.4	)		—			—			(1.3	)		—			—
Unamortized debt (discount) and premium, net		(11.8	)		(4.4	)		(6.9	)		(12.8	)		(4.8	)		(7.4	)
Long-term debt, net	$	2,703.1		$	1,309.0		$	1,082.2		$	2,703.4		$	1,308.6		$	1,081.7

Schedule Of Debt Maturities

	2012		2013		2014		2015		2016
IPL	$	—	$	—	$	38	$	150	$	—
WPL		—		—		8		31		—
Resources		1		1		2		2		3
Alliant Energy parent company		—		—		250		—		—
Alliant Energy	$	1	$	1	$	298	$	183	$	3

Schedule Of Unamortized Debt Issuance Costs

	Alliant Energy				IPL				WPL
	2011		2010		2011		2010		2011		2010
Unamortized debt issuance costs	$	19.1	$	21.2	$	9.0	$	10.0	$	8.4	$	9.1