Fair Value Measurements (Tables)

3 Months Ended

Mar. 31, 2012

Fair Value Measurements [Abstract]

Fair Value Of Financial Instruments

	Alliant Energy				IPL				WPL
	Carrying Amount		Fair Value		Carrying Amount		Fair Value		Carrying Amount		Fair Value
March 31, 2012
Assets:
Money market fund investments	$	21.3	$	21.3	$	21.3	$	21.3	$	—	$	—
Derivative assets (Note 10)		10.4		10.4		5.9		5.9		4.5		4.5
Deferred proceeds (sales of receivables) (Note 3)		32.9		32.9		32.9		32.9		—		—
Capitalization and liabilities:
Long-term debt (including current maturities) (Note 7(b))		2,729.6		3,317.0		1,334.1		1,582.0		1,082.3		1,409.0
Cumulative preferred stock of subsidiaries		205.1		220.6		145.1		161.4		60.0		59.2
Derivative liabilities (Note 10)		83.2		83.2		38.1		38.1		45.1		45.1
Dec. 31, 2011
Assets:
Derivative assets (Note 10)		15.7		15.7		10.6		10.6		5.1		5.1
Deferred proceeds (sales of receivables) (Note 3)		53.7		53.7		53.7		53.7		—		—
Capitalization and liabilities:
Long-term debt (including current maturities) (Note 7(b))		2,704.5		3,325.3		1,309.0		1,560.4		1,082.2		1,439.0
Cumulative preferred stock of subsidiaries		205.1		222.5		145.1		164.3		60.0		58.2
Derivative liabilities (Note 10)		78.0		78.0		33.6		33.6		44.4		44.4

Recurring Fair Value Measurements

	March 31, 2012								Dec. 31, 2011
Alliant Energy	Fair Value		Level 1		Level 2		Level 3		Fair Value		Level 1		Level 2		Level 3
Assets:
Money market fund investments	$	21.3		21.3	$	—	$	—	$	—	$	—	$	—	$	—
Derivatives—commodity contracts		10.4		—		4.9		5.5		15.7		—		3.4		12.3
Deferred proceeds		32.9		—		—		32.9		53.7		—		—		53.7
Capitalization and liabilities:
Long-term debt (including current maturities)		3,317.0		—		3,316.5		0.5		N/A		N/A		N/A		N/A
Cumulative preferred stock of subsidiaries		220.6		171.1		49.5		—		N/A		N/A		N/A		N/A
Derivatives—commodity contracts		83.2		—		62.6		20.6		78.0		—		64.8		13.2

	March 31, 2012								Dec. 31, 2011
IPL	Fair Value		Level 1		Level 2		Level 3		Fair Value		Level 1		Level 2		Level 3
Assets:
Money market fund investments	$	21.3	$	21.3	$	—	$	—	$	—	$	—	$	—	$	—
Derivatives—commodity contracts		5.9		—		2.3		3.6		10.6		—		1.3		9.3
Deferred proceeds		32.9		—		—		32.9		53.7		—		—		53.7
Capitalization and liabilities:
Long-term debt		1,582.0		—		1,582.0		—		N/A		N/A		N/A		N/A
Cumulative preferred stock		161.4		161.4		—		—		N/A		N/A		N/A		N/A
Derivatives—commodity contracts		38.1		—		23.1		15.0		33.6		—		28.6		5.0

	March 31, 2012								Dec. 31, 2011
WPL	Fair Value		Level 1		Level 2		Level 3		Fair Value		Level 1		Level 2		Level 3
Assets:
Derivatives—commodity contracts	$	4.5	$	—	$	2.6	$	1.9	$	5.1	$	—	$	2.1	$	3.0
Capitalization and liabilities:
Long-term debt		1,409.0		—		1,409.0		—		N/A		N/A		N/A		N/A
Cumulative preferred stock		59.2		9.7		49.5		—		N/A		N/A		N/A		N/A
Derivatives—commodity contracts		45.1		—		39.5		5.6		44.4		—		36.2		8.2

Fair Value Measurements Using Significant Unobservable Inputs

	Derivative Assets and (Liabilities), net
	Commodity Contracts						Foreign Contracts					Deferred Proceeds
Alliant Energy	2012			2011			2012		2011			2012			2011
Beginning balance, Jan. 1	($	0.9	)	$	2.8		$	—	$	4.7		$	53.7		$	152.9
Total losses (realized/unrealized) included in changes in net assets (a)		(12.5	)		(0.5	)		—		—			—			—
Transfers into Level 3 (b)		(3.8	)		—			—		—			—			—
Transfers out of Level 3 (c)		5.3			—			—		—			—			—
Settlements (d)		(3.2	)		(3.4	)		—		(2.6	)		(20.8	)		(23.1	)
Ending balance, March 31	($	15.1	)	($	1.1	)	$	—	$	2.1		$	32.9		$	129.8
The amount of total losses for the period included in changes in net assets attributable to the change in unrealized losses relating to assets and liabilities held at March 31 (a)	($	12.5	)	($	0.5	)	$	—	$	—		$	—		$	—

	Derivative Assets and (Liabilities), net
	Commodity Contracts						Foreign Contracts					Deferred Proceeds
IPL	2012			2011			2012		2011			2012			2011
Beginning balance, Jan. 1	$	4.3		$	4.3		$	—	$	4.8		$	53.7		$	152.9
Total losses (realized/unrealized) included in changes in net assets (a)		(10.8	)		(0.2	)		—		—			—			—
Transfers into Level 3 (b)		(2.7	)		—			—		—			—			—
Transfers out of Level 3 (c)		0.1			—			—		—			—			—
Settlements (d)		(2.3	)		(2.7	)		—		(2.7	)		(20.8	)		(23.1	)
Ending balance, March 31	($	11.4	)	$	1.4		$	—	$	2.1		$	32.9		$	129.8
The amount of total losses for the period included in changes in net assets attributable to the change in unrealized losses relating to assets and liabilities held at March 31 (a)	($	10.8	)	($	0.2	)	$	—	$	—		$	—		$	—

	Derivative Assets and (Liabilities), net
	Commodity Contracts						Foreign Contracts
WPL	2012			2011			2012		2011
Beginning balance, Jan. 1	($	5.2	)	($	1.5	)	$	—	($	0.1	)
Total losses (realized/unrealized) included in changes in net assets (a)		(1.7	)		(0.3	)		—		—
Transfers into Level 3 (b)		(1.1	)		—			—		—
Transfers out of Level 3 (c)		5.2			—			—		—
Settlements		(0.9	)		(0.7	)		—		0.1
Ending balance, March 31	($	3.7	)	($	2.5	)	$	—	$	—
The amount of total losses for the period included in changes in net assets attributable to the change in unrealized losses relating to assets and liabilities held at March 31 (a)	($	1.7	)	($	0.3	)	$	—	$	—

(a) Losses related to derivative assets and derivative liabilities are recorded in "Regulatory assets" and "Regulatory liabilities" on the Condensed Consolidated Balance Sheets.

(b) Markets for similar assets and liabilities were not active and observable market inputs were not available for transfers into Level 3. The transfers were valued as of the beginning of the period.

(c) Observable market inputs became available for certain commodity contracts previously classified as Level 3 for transfers out of Level 3. The transfers were valued as of the beginning of the period.

(d) Settlements related to deferred proceeds are due to the change in the carrying amount of receivables sold less the allowance for doubtful accounts associated with the receivables sold and cash proceeds received from the receivables sold.