Benefit Plans (Tables)

3 Months Ended

Mar. 31, 2013

Defined Benefit Plan Disclosure [Line Items]

Defined Benefit Pension And Other Postretirement Benefits Plans

The components of net periodic benefit costs (credits) for Alliant Energy’s, IPL’s and WPL’s sponsored defined benefit pension and other postretirement benefits plans for the three months ended March 31 are included in the tables below (in millions). In the “IPL” and “WPL” tables below, the defined benefit pension plans costs represent those respective costs for IPL’s and WPL’s bargaining unit employees covered under the qualified plans that are sponsored by IPL and WPL, respectively, as well as 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 the Alliant Energy and Corporate Services sponsored qualified and non-qualified defined benefit pension plans. Also in the “IPL” and “WPL” tables below, the other postretirement benefits plans costs (credits) represent costs (credits) for all IPL and WPL employees, respectively.

Alliant Energy	Defined Benefit Pension Plans						Other Postretirement Benefits Plans
	2013			2012			2013			2012
Service cost		$3.9			$3.3			$1.6			$1.7
Interest cost	12.3			13.0			2.1			2.6
Expected return on plan assets	(18.5		)	(17.2		)	(2.0		)	(1.9		)
Amortization of prior service cost (credit)	0.1			0.1			(3.0		)	(3.0		)
Amortization of actuarial loss	9.0			8.3			1.2			1.6
		$6.8			$7.5			($0.1	)		$1.0

IPL	Defined Benefit Pension Plans						Other Postretirement Benefits Plans
	2013			2012			2013			2012
Service cost		$2.2			$1.9			$0.7			$0.8
Interest cost	5.7			6.1			0.9			1.1
Expected return on plan assets	(8.8		)	(8.2		)	(1.4		)	(1.3		)
Amortization of prior service credit	—			—			(1.6		)	(1.6		)
Amortization of actuarial loss	3.8			3.5			0.7			0.9
		$2.9			$3.3			($0.7	)		($0.1	)

WPL	Defined Benefit Pension Plans						Other Postretirement Benefits Plans
	2013			2012			2013			2012
Service cost		$1.4			$1.3			$0.6			$0.7
Interest cost	5.2			5.4			0.8			1.0
Expected return on plan assets	(8.0		)	(7.4		)	(0.3		)	(0.3		)
Amortization of prior service cost (credit)	0.1			—			(1.0		)	(1.0		)
Amortization of actuarial loss	4.3			4.0			0.5			0.6
		$3.0			$3.3			$0.6			$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 (credits) associated with Corporate Services employees providing services to IPL and WPL for the three months ended March 31 (in millions):

	Pension Benefits Costs				Other Postretirement Benefits Credits
	2013		2012		2013			2012
IPL		$0.5		$0.5		($0.1	)		$—
WPL	0.3		0.3		—			—

Estimated Future And Actual Employer Contributions

Estimated and actual funding for the qualified and non-qualified defined benefit pension and other postretirement benefits plans for 2013 are as follows (in millions):

	Estimated for Calendar Year 2013						Actual Through March 31, 2013
	Alliant Energy		IPL		WPL		Alliant Energy		IPL		WPL
Defined benefit pension plans (a)		$2.4		$0.8		$0.2		$0.9		$0.3		$0.1
Other postretirement benefits plans	3.0		—		3.0		—		—		—

(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. In addition, IPL and WPL amounts reflect funding for their non-bargaining employees who are participants in the Alliant Energy and Corporate Services sponsored qualified and non-qualified defined benefit pension plans.

Employees Participate In Defined Contribution Retirement Plans

For the three months ended March 31, 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)
	2013		2012		2013		2012		2013		2012
401(k) costs		$5.4		$5.2		$2.8		$2.7		$2.3		$2.3

(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 months ended March 31 was as follows (in millions):

	Alliant Energy				IPL				WPL
	2013		2012		2013		2012		2013		2012
Compensation expense		$2.7		$1.6		$1.4		$0.8		$1.1		$0.7
Income tax benefits	1.1		0.6		0.6		0.3		0.5		0.3

Schedule Of Equity Incentive Plans Activity

Information related to fair values of nonvested performance shares and units at March 31, 2013 by year of grant were as follows:

	Performance Shares									Performance Units
	2013 Grant			2012 Grant			2011 Grant			2013 Grant			2012 Grant			2011 Grant
Nonvested awards	49,093			45,612			45,235			22,201			23,392			20,804
Alliant Energy common stock closing price on March 31, 2013		$50.18			$50.18			$50.18
Alliant Energy common stock closing price on grant date											$47.58			$43.05			$38.75
Estimated payout percentage based on performance criteria	97		%	92		%	112		%	97		%	92		%	112		%
Fair values of each nonvested award		$48.67			$46.17			$56.20			$46.15			$39.61			$43.40

Performance Contingent Restricted Stock [Member]

Defined Benefit Plan Disclosure [Line Items]

Defined Benefit Pension And Other Postretirement Benefits Plans

A summary of the performance-contingent restricted stock activity for the three months ended March 31 was as follows:

	2013				2012
	Shares		Weighted Average Fair Value		Shares		Weighted Average Fair Value
Nonvested shares, January 1	211,651			$32.42	301,738			$32.60
Granted	49,093		47.58		45,612		43.05
Vested (a)	—		—		(65,172	)	32.56
Forfeited (b)	(101,822	)	23.67		(70,527	)	39.93
Nonvested shares, March 31	158,922		42.71		211,651		32.42

(a) In 2012, 65,172 performance-contingent restricted shares granted in 2010 vested because the specified performance criteria for such shares were met.

(b) In 2013 and 2012, 101,822 and 65,516 performance-contingent restricted shares granted in 2009 and 2008, respectively, were forfeited because the specified performance criteria for such shares were not met. The remaining forfeitures during 2012 were primarily caused by retirements and terminations of participants.

Performance Contingent Cash Awards [Member]

Defined Benefit Plan Disclosure [Line Items]

Defined Benefit Pension And Other Postretirement Benefits Plans

A summary of the performance contingent cash awards activity for the three months ended March 31 was as follows:

	2013	2012
	Awards	Awards
Nonvested awards, January 1	59,639	46,676
Granted	39,530	36,936
Vested (a)	—	(21,605	)
Forfeited	—	(1,533	)
Nonvested awards, March 31	99,169	60,474

(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 three months ended March 31 was as follows:

	2013		2012
	Shares (a)		Shares (a)
Nonvested shares, January 1	145,277		236,979
Granted	49,093		45,612
Vested (b)	(54,430	)	(111,980	)
Nonvested shares, March 31	139,940		170,611

(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 2013, 54,430 performance shares granted in 2010 vested at 197.5% of the target, resulting in payouts valued at $4.8 million, which consisted of a combination of cash and common stock (4,177 shares). 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).

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 three months ended March 31 was as follows:

	2013		2012
	Units (a)		Units (a)
Nonvested units, January 1	64,969		42,996
Granted	22,201		24,686
Vested (b)	(19,760	)	—
Forfeited	(1,013	)	(878	)
Nonvested units, March 31	66,397		66,804

(a) Unit amounts represent the target number of performance units. Each performance unit’s value is based on the closing 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.

(b) In the first quarter of 2013, 19,760 performance units granted in 2010 vested at 197.5% of the target, resulting in cash payouts valued at $1.3 million.

IPL [Member]

Defined Benefit Plan Disclosure [Line Items]

Defined Benefit Pension And Other Postretirement Benefits Plans

The components of net periodic benefit costs (credits) for Alliant Energy’s, IPL’s and WPL’s sponsored defined benefit pension and other postretirement benefits plans for the three months ended March 31 are included in the tables below (in millions). In the “IPL” and “WPL” tables below, the defined benefit pension plans costs represent those respective costs for IPL’s and WPL’s bargaining unit employees covered under the qualified plans that are sponsored by IPL and WPL, respectively, as well as 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 the Alliant Energy and Corporate Services sponsored qualified and non-qualified defined benefit pension plans. Also in the “IPL” and “WPL” tables below, the other postretirement benefits plans costs (credits) represent costs (credits) for all IPL and WPL employees, respectively.

Alliant Energy	Defined Benefit Pension Plans						Other Postretirement Benefits Plans
	2013			2012			2013			2012
Service cost		$3.9			$3.3			$1.6			$1.7
Interest cost	12.3			13.0			2.1			2.6
Expected return on plan assets	(18.5		)	(17.2		)	(2.0		)	(1.9		)
Amortization of prior service cost (credit)	0.1			0.1			(3.0		)	(3.0		)
Amortization of actuarial loss	9.0			8.3			1.2			1.6
		$6.8			$7.5			($0.1	)		$1.0

IPL	Defined Benefit Pension Plans						Other Postretirement Benefits Plans
	2013			2012			2013			2012
Service cost		$2.2			$1.9			$0.7			$0.8
Interest cost	5.7			6.1			0.9			1.1
Expected return on plan assets	(8.8		)	(8.2		)	(1.4		)	(1.3		)
Amortization of prior service credit	—			—			(1.6		)	(1.6		)
Amortization of actuarial loss	3.8			3.5			0.7			0.9
		$2.9			$3.3			($0.7	)		($0.1	)

WPL	Defined Benefit Pension Plans						Other Postretirement Benefits Plans
	2013			2012			2013			2012
Service cost		$1.4			$1.3			$0.6			$0.7
Interest cost	5.2			5.4			0.8			1.0
Expected return on plan assets	(8.0		)	(7.4		)	(0.3		)	(0.3		)
Amortization of prior service cost (credit)	0.1			—			(1.0		)	(1.0		)
Amortization of actuarial loss	4.3			4.0			0.5			0.6
		$3.0			$3.3			$0.6			$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 (credits) associated with Corporate Services employees providing services to IPL and WPL for the three months ended March 31 (in millions):

	Pension Benefits Costs				Other Postretirement Benefits Credits
	2013		2012		2013			2012
IPL		$0.5		$0.5		($0.1	)		$—
WPL	0.3		0.3		—			—

Estimated Future And Actual Employer Contributions

Estimated and actual funding for the qualified and non-qualified defined benefit pension and other postretirement benefits plans for 2013 are as follows (in millions):

	Estimated for Calendar Year 2013						Actual Through March 31, 2013
	Alliant Energy		IPL		WPL		Alliant Energy		IPL		WPL
Defined benefit pension plans (a)		$2.4		$0.8		$0.2		$0.9		$0.3		$0.1
Other postretirement benefits plans	3.0		—		3.0		—		—		—

(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. In addition, IPL and WPL amounts reflect funding for their non-bargaining employees who are participants in the Alliant Energy and Corporate Services sponsored qualified and non-qualified defined benefit pension plans.

Employees Participate In Defined Contribution Retirement Plans

For the three months ended March 31, 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)
	2013		2012		2013		2012		2013		2012
401(k) costs		$5.4		$5.2		$2.8		$2.7		$2.3		$2.3

(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 months ended March 31 was as follows (in millions):

	Alliant Energy				IPL				WPL
	2013		2012		2013		2012		2013		2012
Compensation expense		$2.7		$1.6		$1.4		$0.8		$1.1		$0.7
Income tax benefits	1.1		0.6		0.6		0.3		0.5		0.3

WPL [Member]

Defined Benefit Plan Disclosure [Line Items]

Defined Benefit Pension And Other Postretirement Benefits Plans

The components of net periodic benefit costs (credits) for Alliant Energy’s, IPL’s and WPL’s sponsored defined benefit pension and other postretirement benefits plans for the three months ended March 31 are included in the tables below (in millions). In the “IPL” and “WPL” tables below, the defined benefit pension plans costs represent those respective costs for IPL’s and WPL’s bargaining unit employees covered under the qualified plans that are sponsored by IPL and WPL, respectively, as well as 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 the Alliant Energy and Corporate Services sponsored qualified and non-qualified defined benefit pension plans. Also in the “IPL” and “WPL” tables below, the other postretirement benefits plans costs (credits) represent costs (credits) for all IPL and WPL employees, respectively.

Alliant Energy	Defined Benefit Pension Plans						Other Postretirement Benefits Plans
	2013			2012			2013			2012
Service cost		$3.9			$3.3			$1.6			$1.7
Interest cost	12.3			13.0			2.1			2.6
Expected return on plan assets	(18.5		)	(17.2		)	(2.0		)	(1.9		)
Amortization of prior service cost (credit)	0.1			0.1			(3.0		)	(3.0		)
Amortization of actuarial loss	9.0			8.3			1.2			1.6
		$6.8			$7.5			($0.1	)		$1.0

IPL	Defined Benefit Pension Plans						Other Postretirement Benefits Plans
	2013			2012			2013			2012
Service cost		$2.2			$1.9			$0.7			$0.8
Interest cost	5.7			6.1			0.9			1.1
Expected return on plan assets	(8.8		)	(8.2		)	(1.4		)	(1.3		)
Amortization of prior service credit	—			—			(1.6		)	(1.6		)
Amortization of actuarial loss	3.8			3.5			0.7			0.9
		$2.9			$3.3			($0.7	)		($0.1	)

WPL	Defined Benefit Pension Plans						Other Postretirement Benefits Plans
	2013			2012			2013			2012
Service cost		$1.4			$1.3			$0.6			$0.7
Interest cost	5.2			5.4			0.8			1.0
Expected return on plan assets	(8.0		)	(7.4		)	(0.3		)	(0.3		)
Amortization of prior service cost (credit)	0.1			—			(1.0		)	(1.0		)
Amortization of actuarial loss	4.3			4.0			0.5			0.6
		$3.0			$3.3			$0.6			$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 (credits) associated with Corporate Services employees providing services to IPL and WPL for the three months ended March 31 (in millions):

	Pension Benefits Costs				Other Postretirement Benefits Credits
	2013		2012		2013			2012
IPL		$0.5		$0.5		($0.1	)		$—
WPL	0.3		0.3		—			—

Estimated Future And Actual Employer Contributions

Estimated and actual funding for the qualified and non-qualified defined benefit pension and other postretirement benefits plans for 2013 are as follows (in millions):

	Estimated for Calendar Year 2013						Actual Through March 31, 2013
	Alliant Energy		IPL		WPL		Alliant Energy		IPL		WPL
Defined benefit pension plans (a)		$2.4		$0.8		$0.2		$0.9		$0.3		$0.1
Other postretirement benefits plans	3.0		—		3.0		—		—		—

(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. In addition, IPL and WPL amounts reflect funding for their non-bargaining employees who are participants in the Alliant Energy and Corporate Services sponsored qualified and non-qualified defined benefit pension plans.

Employees Participate In Defined Contribution Retirement Plans

For the three months ended March 31, 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)
	2013		2012		2013		2012		2013		2012
401(k) costs		$5.4		$5.2		$2.8		$2.7		$2.3		$2.3

(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 months ended March 31 was as follows (in millions):

	Alliant Energy				IPL				WPL
	2013		2012		2013		2012		2013		2012
Compensation expense		$2.7		$1.6		$1.4		$0.8		$1.1		$0.7
Income tax benefits	1.1		0.6		0.6		0.3		0.5		0.3