Fair Value Measurements (Tables)

12 Months Ended

Dec. 31, 2011

Fair Value Measurements [Abstract]

Fair Value Of Financial Instruments

	Alliant Energy				IPL				WPL
	Carrying		Fair		Carrying		Fair		Carrying		Fair
	Amount		Value		Amount		Value		Amount		Value
2011
Assets:
Derivative assets (Note 12)	$	15.7	$	15.7	$	10.6	$	10.6	$	5.1	$	5.1
Deferred proceeds (sales of receivables) (Note 4(a))		53.7		53.7		53.7		53.7		—		—
Capitalization and liabilities:
Long-term debt (including current maturities) (Note 9(b))		2,704.5		3,325.3		1,309.0		1,560.4		1,082.2		1,439.0
Cumulative preferred stock of subsidiaries (Note 8)		205.1		222.5		145.1		164.3		60.0		58.2
Derivative liabilities (Note 12)		78.0		78.0		33.6		33.6		44.4		44.4
2010
Assets:
Money market fund investments (Note 1(d))		128.3		128.3		5.6		5.6		—		—
Derivative assets (Note 12)		20.9		20.9		12.9		12.9		8.0		8.0
Deferred proceeds (sales of receivables) (Note 4(a))		152.9		152.9		152.9		152.9		—		—
Capitalization and liabilities:
Long-term debt (including current maturities) (Note 9(b))		2,704.7		2,958.6		1,308.6		1,417.0		1,081.7		1,219.6
Cumulative preferred stock of subsidiaries (Note 8)		243.8		266.7		183.8		210.7		60.0		56.0
Derivative liabilities (Note 12)		67.3		67.3		24.0		24.0		43.3		43.3

Recurring Fair Value Measurements

	2011								2010
	Fair Value		Level 1		Level 2		Level 3		Fair Value		Level 1		Level 2		Level 3
Assets:
Money market fund investments	$	—	$	—	$	—	$	—	$	128.3	$	128.3	$	—	$	—
Derivative assets:
Commodity contracts		15.7		—		3.4		12.3		16.1		—		10.0		6.1
Foreign exchange contracts		—		—		—		—		4.8		—		—		4.8
Total derivative assets		15.7		—		3.4		12.3		20.9		—		10.0		10.9
Deferred proceeds		53.7		—		—		53.7		152.9		—		—		152.9
Liabilities:
Derivative liabilities:
Commodity contracts		78.0		—		64.8		13.2		67.2		—		63.9		3.3
Foreign exchange contracts		—		—		—		—		0.1		—		—		0.1
Total derivative liabilities		78.0		—		64.8		13.2		67.3		—		63.9		3.4
IPL
	2011								2010
	Fair Value		Level 1		Level 2		Level 3		Fair Value		Level 1		Level 2		Level 3
Assets:
Money market fund investments	$	—	$	—	$	—	$	—	$	5.6	$	5.6	$	—	$	—
Derivative assets:
Commodity contracts		10.6		—		1.3		9.3		8.1		—		3.6		4.5
Foreign exchange contracts		—		—		—		—		4.8		—		—		4.8
Total derivative assets		10.6		—		1.3		9.3		12.9		—		3.6		9.3
Deferred proceeds		53.7		—		—		53.7		152.9		—		—		152.9
Liabilities:
Derivative liabilities:
Commodity contracts		33.6		—		28.6		5.0		24.0		—		23.8		0.2
WPL
	2011								2010
	Fair Value		Level 1		Level 2		Level 3		Fair Value		Level 1		Level 2		Level 3
Assets:
Derivative assets:
Commodity contracts	$	5.1	$	—	$	2.1	$	3.0	$	8.0	$	—	$	6.4	$	1.6
Liabilities:
Derivative liabilities:
Commodity contracts		44.4		—		36.2		8.2		43.2		—		40.1		3.1
Foreign exchange contracts		—		—		—		—		0.1		—		—		0.1
Total derivative liabilities		44.4		—		36.2		8.2		43.3		—		40.1		3.2

Fair Value Measurements Using Significant Unobservable Inputs

	Derivative Assets and (Liabilities), net
	Commodity Contracts						Foreign Contracts						Deferred Proceeds
	2011			2010			2011			2010			2011			2010
Beginning balance, Jan. 1	$	2.8		$	2.6		$	4.7		$	3.1		$	152.9		$	—
Total gains (losses) (realized/unrealized) included in changes in net assets (a)		(7.3	)		(0.8	)		—			3.8			—			—
Transfers in and/or out of Level 3 (b)		0.2			(0.3	)		—			—			—			—
Purchases		21.8			—			—			—			—			—
Settlements (c)		(18.4	)		1.3			(4.7	)		(2.2	)		(99.2	)		152.9
Ending balance, Dec. 31		($0.9	)	$	2.8		$	—		$	4.7		$	53.7		$	152.9
	Derivative Assets and (Liabilities), net
	Commodity Contracts						Foreign Contracts						Deferred Proceeds
	2011			2010			2011			2010			2011			2010
The amount of total gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at Dec. 31 (a)		($7.3	)		($0.8	)	$	—		$	3.8		$	—		$	—

IPL

	Derivative Assets and (Liabilities), net
	Commodity					Foreign						Deferred
	Contracts					Contracts						Proceeds
	2011			2010		2011			2010			2011			2010
Beginning balance, Jan. 1	$	4.3		$	1.4	$	4.8		$	4.6		$	152.9		$	—
Total gains (losses) (realized/unrealized) included in changes in net assets (a)		(3.1	)		0.5		—			3.8			—			—
Purchases		18.1			—		—			—			—			—
Sales (d)		—			—		(2.1	)		—			—			—
Settlements (c)		(15.0	)		2.4		(2.7	)		(3.6	)		(99.2	)		152.9
Ending balance, Dec. 31	$	4.3		$	4.3	$	—		$	4.8		$	53.7		$	152.9
The amount of total gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at Dec. 31 (a)		($3.1	)	$	0.5	$	—		$	3.8		$	—		$	—

WPL

	Derivative Assets and (Liabilities), net
	Commodity						Foreign
	Contracts						Contracts
	2011			2010			2011			2010
Beginning balance, Jan. 1		($1.5	)	$	1.2			($0.1	)		($1.5	)
Total losses (realized/unrealized) included in changes in net assets (a)		(4.2	)		(1.3	)		—			—
Transfers in and/or out of Level 3 (b)		0.2			(0.3	)		—			—
Purchases		3.7			—			—			—
Settlements		(3.4	)		(1.1	)		0.1			1.4
Ending balance, Dec. 31		($5.2	)		($1.5	)	$	—			($0.1	)
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 Dec. 31 (a)		($4.2	)		($1.3	)	$	—		$	—

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

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

(c) 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.

(d) The foreign exchange contract was transferred from IPL to Resources in connection with the sale of wind project assets in 2011.