Benefit Plans (Tables)

6 Months Ended

Jun. 30, 2012

Defined Benefit Plan Disclosure [Line Items]

Defined Benefit Pension And Other Postretirement Benefits Plans

The “Directly assigned defined benefit pension plans” tables below include amounts directly assigned to each of IPL and WPL related to IPL’s and WPL’s current and former non-bargaining employees who are participants in Alliant Energy and Corporate Services sponsored qualified and non-qualified defined benefit pension plans.

Alliant Energy	Defined Benefit Pension Plans												Other Postretirement Benefits Plans
	Three Months						Six Months						Three Months						Six Months
	2012			2011			2012			2011			2012			2011			2012			2011
Service cost		$3.4			$2.8			$6.7			$5.7			$1.8			$1.7			$3.5			$3.8
Interest cost	12.9			13.0			25.9			26.0			2.5			3.1			5.1			6.7
Expected return on plan assets	(17.2		)	(15.9		)	(34.4		)	(31.9		)	(1.9		)	(2.0		)	(3.8		)	(3.9		)
Amortization of:
Prior service cost (credit)	—			0.2			0.1			0.4			(3.0		)	(2.5		)	(6.0		)	(3.2		)
Actuarial loss	8.3			5.3			16.6			10.5			1.5			1.4			3.1			2.8
Additional benefit costs (a)	—			8.9			—			8.9			—			—			—			—
		$7.4			$14.3			$14.9			$19.6			$0.9			$1.7			$1.9			$6.2

IPL	Qualified Defined Benefit Pension Plans												Other Postretirement Benefits Plans
	Three Months						Six Months						Three Months						Six Months
	2012			2011			2012			2011			2012			2011			2012			2011
Service cost		$1.9			$1.5			$3.8			$3.1			$0.7			$0.6			$1.5			$1.4
Interest cost	4.2			4.1			8.5			8.3			1.1			1.3			2.2			3.0
Expected return on plan assets	(5.7		)	(5.0		)	(11.5		)	(10.0		)	(1.3		)	(1.3		)	(2.6		)	(2.6		)
Amortization of:
Prior service cost (credit)	0.1			0.1			0.2			0.2			(1.6		)	(1.2		)	(3.2		)	(1.5		)
Actuarial loss	2.6			1.5			5.1			2.9			0.9			0.7			1.8			1.5
		$3.1			$2.2			$6.1			$4.5			($0.2	)		$0.1			($0.3	)		$1.8

WPL	Qualified Defined Benefit Pension Plan												Other Postretirement Benefits Plans
	Three Months						Six Months						Three Months						Six Months
	2012			2011			2012			2011			2012			2011			2012			2011
Service cost		$1.3			$1.1			$2.6			$2.3			$0.7			$0.7			$1.4			$1.5
Interest cost	4.1			4.0			8.2			8.0			1.1			1.2			2.1			2.6
Expected return on plan assets	(5.6		)	(5.0		)	(11.2		)	(10.0		)	(0.4		)	(0.4		)	(0.7		)	(0.7		)
Amortization of:
Prior service cost (credit)	0.1			0.2			0.2			0.3			(0.9		)	(0.8		)	(1.9		)	(1.1		)
Actuarial loss	3.0			1.7			6.1			3.5			0.5			0.6			1.1			1.1
		$2.9			$2.0			$5.9			$4.1			$1.0			$1.3			$2.0			$3.4

Directly assigned defined benefit pension plans	IPL												WPL
	Three Months						Six Months						Three Months						Six Months
	2012			2011			2012			2011			2012			2011			2012			2011
Interest cost		$1.7			$1.8			$3.5			$3.7			$1.3			$1.3			$2.6			$2.7
Expected return on plan assets	(2.4		)	(2.5		)	(4.8		)	(4.9		)	(1.8		)	(1.8		)	(3.6		)	(3.6		)
Amortization of:
Prior service credit	—			—			(0.1		)	(0.1		)	—			—			(0.1		)	(0.1		)
Actuarial loss	0.9			0.8			1.9			1.5			0.9			0.7			1.8			1.4
Additional benefit costs (a)	—			2.2			—			2.2			—			0.6			—			0.6
		$0.2			$2.3			$0.5			$2.4			$0.4			$0.8			$0.7			$1.0

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

The following table includes the allocated qualified and non-qualified pension and other postretirement benefits costs associated with Corporate Services employees providing services to IPL and WPL for the three and six months ended June 30 (in millions):

	Pension Benefits Costs (a)								Other Postretirement Benefits Costs
	Three Months				Six Months				Three Months				Six Months
	2012		2011		2012		2011		2012		2011		2012		2011
IPL		$0.5		$3.7		$1.0		$4.1		$0.1		$—		$0.1		$0.4
WPL	0.3		2.7		0.6		3.0		—		0.1		—		0.3

Estimated Future And Actual Employer Contributions

Estimated and actual funding for the qualified defined benefit pension, non-qualified defined benefit pension and other postretirement benefits plans, and the directly assigned qualified and non-qualified defined benefit pension plans amounts for 2012 are as follows (in millions):

	Estimated for Calendar Year 2012						Actual Through June 30, 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		2.6		N/A		N/A
Directly assigned defined benefit pension plans (b)	N/A		0.8		0.2		N/A		0.4		0.1
Other postretirement benefits plans	6.5		2.2		3.9		3.7		1.5		2.0

(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

For the three and six months ended June 30, costs related to the 401(k) savings plans, which are partially based on the participants’ level of contribution, were as follows (in millions):

	Alliant Energy								IPL (a)								WPL (a)
	Three Months				Six Months				Three Months				Six Months				Three Months				Six Months
	2012		2011		2012		2011		2012		2011		2012		2011		2012		2011		2012		2011
401(k) costs		$4.5		$4.2		$9.7		$9.9		$2.3		$2.0		$5.0		$4.9		$1.9		$2.0		$4.2		$4.6

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

Recognized Compensation Expense And Income Tax Benefits

A summary of compensation expense and the related income tax benefits recognized for share-based compensation awards for the three and six months ended June 30 was as follows (in millions):

	Alliant Energy								IPL								WPL
	Three Months				Six Months				Three Months				Six Months				Three Months				Six Months
	2012		2011		2012		2011		2012		2011		2012		2011		2012		2011		2012		2011
Compensation expense		$2.1		$2.6		$3.7		$4.8		$1.1		$1.4		$1.9		$2.6		$0.9		$1.0		$1.6		$1.9
Income tax benefits	0.9		1.0		1.5		1.9		0.5		0.5		0.8		1.0		0.3		0.4		0.6		0.8

Schedule Of Equity Incentive Plans Activity

Information related to fair values of nonvested performance shares and units at June 30, 2012 by year of grant, were as follows:

	Performance Shares									Performance Units
	2012			2011			2010			2012			2011			2010
	Grant			Grant			Grant			Grant			Grant			Grant
Nonvested awards	45,612			45,235			54,430			24,686			21,693			20,425
Alliant Energy common stock closing price on June 30, 2012		$45.57			$45.57			$45.57
Alliant Energy common stock average price on grant date											$43.05			$38.75			$32.56
Estimated payout percentage based on performance criteria	93		%	108		%	176		%	93		%	108		%	176		%
Fair values of each nonvested award		$42.38			$49.22			$80.20			$40.04			$41.85			$57.30

Disclosure Of Other Stock Option Activity

Other information related to stock option activity for the three and six months ended June 30 was as follows (in millions):

	Three Months				Six Months
	2012		2011		2012		2011
Cash received from stock options exercised		$0.4		$1.0		$0.7		$1.6
Aggregate intrinsic value of stock options exercised	0.3		0.6		0.5		0.8
Income tax benefit from the exercise of stock options	0.1		0.2		0.2		0.3

Time-Based Restricted Stock [Member]

Defined Benefit Plan Disclosure [Line Items]

Defined Benefit Pension And Other Postretirement Benefits Plans

Time-based restricted stock - A summary of the time-based restricted stock activity for the six months ended June 30 was as follows:

	2012				2011
	Shares		Weighted Average Fair Value		Shares		Weighted Average Fair Value
Nonvested shares, January 1	35,800			$30.87	70,033			$32.27
Granted during first quarter	—		—		5,000		39.86
Vested	(32,466	)	29.95		(38,433	)	34.61
Forfeited	—		—		(600	)	29.41
Nonvested shares, June 30	3,334		39.86		36,000		30.88

Performance-Contingent Restricted Stock [Member]

Defined Benefit Plan Disclosure [Line Items]

Defined Benefit Pension And Other Postretirement Benefits Plans

Performance-contingent restricted stock - A summary of the performance-contingent restricted stock activity for the six months ended June 30 was as follows:

	2012				2011
	Shares		Weighted Average Fair Value		Shares		Weighted Average Fair Value
Nonvested shares, January 1	301,738			$32.60	296,190			$32.32
Granted during first quarter	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, June 30	211,651		32.42		301,738		32.60

Non-Qualified Stock Options [Member]

Defined Benefit Plan Disclosure [Line Items]

Defined Benefit Pension And Other Postretirement Benefits Plans

Non-qualified Stock Options - A summary of the stock option activity for the six months ended June 30 was as follows:

	2012				2011
	Shares		Weighted Average Exercise Price		Shares		Weighted Average Exercise Price
Outstanding, January 1	63,889			$24.21	163,680			$24.51
Exercised	(27,453	)	23.79		(60,481	)	27.08
Outstanding and exercisable, June 30	36,436		24.52		103,199		23.01

Performance Contingent Cash Awards [Member]

Defined Benefit Plan Disclosure [Line Items]

Defined Benefit Pension And Other Postretirement Benefits Plans

Performance Contingent Cash Awards - A summary of the performance contingent cash awards activity for the six months ended June 30 was as follows:

	2012		2011
	Awards		Awards
Nonvested awards, January 1	46,676		23,428
Granted	36,936		23,975
Vested (a)	(21,605	)	—
Forfeited	(1,533	)	(727	)
Nonvested awards, June 30	60,474		46,676

(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

A summary of the performance shares activity for the six months ended June 30 was as follows:

	2012		2011
	Shares (a)		Shares (a)
Nonvested shares, January 1	236,979		234,518
Granted	45,612		64,217
Vested (b)	(111,980	)	(57,838	)
Forfeited	(25,334	)	—
Nonvested shares, June 30	145,277		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

Performance Units [Member]

Defined Benefit Plan Disclosure [Line Items]

Defined Benefit Pension And Other Postretirement Benefits Plans

A summary of the performance unit activity for the six months ended June 30 was as follows:

	2012		2011
	Units (a)		Units (a)
Nonvested units, January 1	42,996		23,128
Granted	24,686		23,975
Forfeited	(878	)	(4,107	)
Nonvested units, June 30	66,804		42,996

(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