Benefit Plans (Tables)

3 Months Ended

Mar. 31, 2012

Defined Benefit Plan Disclosure [Line Items]

Defined Benefit Pension And Other Postretirement Benefits Plans

Alliant Energy	Defined Benefit Pension Plans						Other Postretirement Benefits Plans
	2012			2011			2012			2011
Service cost	$	3.3		$	2.9		$	1.7		$	2.1
Interest cost		13.0			13.0			2.6			3.6
Expected return on plan assets		(17.2	)		(16.0	)		(1.9	)		(1.9	)
Amortization of:
Prior service cost (credit)		0.1			0.2			(3.0	)		(0.7	)
Actuarial loss		8.3			5.2			1.6			1.4
	$	7.5		$	5.3		$	1.0		$	4.5

IPL	Qualified Defined Benefit Pension Plans						Other Postretirement Benefits Plans
	2012			2011			2012			2011
Service cost	$	1.9		$	1.6		$	0.8		$	0.8
Interest cost		4.3			4.2			1.1			1.7
Expected return on plan assets		(5.8	)		(5.0	)		(1.3	)		(1.3	)
Amortization of:
Prior service cost (credit)		0.1			0.1			(1.6	)		(0.3	)
Actuarial loss		2.5			1.4			0.9			0.8
	$	3.0		$	2.3		($	0.1	)	$	1.7

WPL	Qualified Defined Benefit Pension Plan						Other Postretirement Benefits Plans
	2012			2011			2012			2011
Service cost	$	1.3		$	1.2		$	0.7		$	0.8
Interest cost		4.1			4.0			1.0			1.4
Expected return on plan assets		(5.6	)		(5.0	)		(0.3	)		(0.3	)
Amortization of:
Prior service cost (credit)		0.1			0.1			(1.0	)		(0.3	)
Actuarial loss		3.1			1.8			0.6			0.5
	$	3.0		$	2.1		$	1.0		$	2.1

Directly assigned defined benefit pension plans	IPL						WPL
	2012			2011			2012			2011
Interest cost	$	1.8		$	1.9		$	1.3		$	1.4
Expected return on plan assets		(2.4	)		(2.4	)		(1.8	)		(1.8	)
Amortization of:
Prior service credit		(0.1	)		(0.1	)		(0.1	)		(0.1	)
Actuarial loss		1.0			0.7			0.9			0.7
	$	0.3		$	0.1		$	0.3		$	0.2

Schedule Of Qualified And Non-Qualified Pension And Other Post Retirement Benefits Costs

	Pension Benefits Costs				Other Postretirement Benefits Costs
	2012		2011		2012		2011
IPL	$	0.5	$	0.4	$	—	$	0.4
WPL		0.3		0.3		—		0.2

Estimated Future And Actual Employer Contributions

			Estimated for Calendar Year 2012							Actual Through March 31, 2012
	Alliant Energy			IPL		WPL		Alliant Energy			IPL		WPL
Qualified defined benefit pension plans	$	—		$	—	$	—	$	—		$	—	$	—
Non-qualified defined benefit pension plans (a)		17.0			N/A		N/A		2.1			N/A		N/A
Directly assigned defined benefit pension plans (b)		N/A			0.8		0.2		N/A			0.2		—
Other postretirement benefits plans		5.4			1.1		3.9		2.2			1.1		1.0

(a) Alliant Energy sponsors several non-qualified defined benefit pension plans that cover certain current and former key employees of IPL and WPL. Alliant Energy allocates pension costs to IPL and WPL for these plans.

(b) Amounts directly assigned to IPL and WPL for non-bargaining employees who are participants in Alliant Energy and Corporate Services sponsored qualified and non-qualified defined benefit pension plans.

Employees Participate In Defined Contribution Retirement Plans

	Alliant Energy				IPL (a)				WPL (a)
	2012		2011		2012		2011		2012		2011
401(k) costs	$	5.2	$	5.7	$	2.7	$	2.9	$	2.3	$	2.6

(a) IPL's and WPL's amounts include allocated costs associated with Corporate Services employees.

Recognized Compensation Expense And Income Tax Benefits

	Alliant Energy				IPL				WPL
	2012		2011		2012		2011		2012		2011
Compensation expense	$	1.6	$	2.2	$	0.8	$	1.2	$	0.7	$	0.9
Income tax benefits		0.6		0.9		0.3		0.5		0.3		0.4

Schedule Of Equity Incentive Plans Activity

	Performance Shares									Performance Units
	2012 Grant			2011 Grant			2010 Grant			2012 Grant			2011 Grant			2010 Grant
Nonvested awards		45,612			62,170			62,829			24,686			21,693			20,425
Alliant Energy common stock closing price on March 31, 2012	$	43.32		$	43.32		$	43.32
Alliant Energy common stock average price on grant date										$	43.05		$	38.75		$	32.56
Estimated payout percentage based on performance criteria		93	%		105	%		161	%		93	%		105	%		161	%
Fair values of each nonvested award	$	40.29		$	45.49		$	69.75		$	40.04		$	40.69		$	52.41

Disclosure Of Other Stock Option Activity

	2012		2011
Cash received from stock options exercised	$	0.3	$	0.6
Aggregate intrinsic value of stock options exercised		0.2		0.2
Income tax benefit from the exercise of stock options		0.1		0.1

Performance-Contingent Restricted Stock [Member]

Defined Benefit Plan Disclosure [Line Items]

Schedule Of Equity Incentive Plans Activity

	2012					2011
	Shares			Weighted Average Fair Value		Shares			Weighted Average Fair Value
Nonvested shares, Jan. 1		301,738		$	32.60		296,190		$	32.32
Granted		45,612			43.05		64,217			38.75
Vested		(65,172	)		32.56		(53,274	)		37.93
Forfeited		(70,527	)		39.93		(5,395	)		38.00
Nonvested shares, March 31		211,651			32.42		301,738			32.60

Non-Qualified Stock Options [Member]

Defined Benefit Plan Disclosure [Line Items]

Schedule Of Equity Incentive Plans Activity

	2012					2011
	Shares			Weighted Average Exercise Price		Shares			Weighted Average Exercise Price
Outstanding, Jan. 1		63,889		$	24.21		163,680		$	24.51
Exercised		(13,400	)		24.83		(20,591	)		27.79
Outstanding and exercisable, March 31		50,489			24.04		143,089			24.04

Time-Based Restricted Stock [Member]

Defined Benefit Plan Disclosure [Line Items]

Schedule Of Equity Incentive Plans Activity

	2012					2011
	Shares			Weighted Average Fair Value		Shares			Weighted Average Fair Value
Nonvested shares, Jan. 1		35,800		$	30.87		70,033		$	32.27
Granted		—			—		5,000			39.86
Vested		(32,466	)		29.95		(33,516	)		35.34
Nonvested shares, March 31		3,334			39.86		41,517			30.71

Performance Contingent Cash Awards [Member]

Defined Benefit Plan Disclosure [Line Items]

Schedule Of Equity Incentive Plans Activity

	2012			2011
	Awards			Awards
Nonvested awards, Jan. 1		46,676			23,428
Granted		36,936			23,975
Vested (a)		(21,605	)		—
Forfeited		(1,533	)		—
Nonvested awards, March 31		60,474			47,403

(a)	In the first quarter of 2012, 21,605 performance contingent cash awards granted in 2010 vested, resulting in cash payouts valued at $0.9 million.

Performance Shares [Member]

Defined Benefit Plan Disclosure [Line Items]

Schedule Of Equity Incentive Plans Activity

	2012			2011
	Shares (a)			Shares (a)
Nonvested shares, Jan. 1		236,979			234,518
Granted		45,612			64,217
Vested (b)		(111,980	)		(57,838	)
Nonvested shares, March 31		170,611			240,897

(a) Share amounts represent the target number of performance shares. Each performance share's value is based on the price of one share of Alliant Energy's common stock at the end of the performance period. The actual number of shares that will be paid out upon vesting is dependent upon actual performance and may range from zero to 200% of the target number of shares.

(b)

In the first quarter of 2012, 111,980 performance shares granted in 2009 vested at 162.5% of the target, resulting in payouts valued at $8.0 million, which consisted of a combination of cash and common stock (6,399 shares). In the first quarter of 2011, 57,838 performance shares granted in 2008 vested at 75% of the target, resulting in payouts valued at $1.6 million, which consisted of a combination of cash and common stock (1,387 shares).

Performance Units [Member]

Defined Benefit Plan Disclosure [Line Items]

Schedule Of Equity Incentive Plans Activity

	2012			2011
	Units (a)			Units (a)
Nonvested units, Jan. 1		42,996			23,128
Granted		24,686			23,975
Forfeited		(878	)		(569	)
Nonvested units, March 31		66,804			46,534

(a) Unit amounts represent the target number of performance units. Each performance unit's value is based on the average price of one share of Alliant Energy's common stock on the grant date of the award. The actual payout for performance units is dependent upon actual performance and may range from zero to 200% of the target number of units.