Benefit Plans (Tables)

3 Months Ended

Mar. 31, 2016

Defined Benefit Plan Disclosure [Line Items]

Defined Benefit Pension And Other Postretirement Benefits Plans

The components of net periodic benefit costs (credits) for sponsored defined benefit pension and OPEB plans for the three months ended March 31 are included in the tables below (in millions). In IPL’s and WPL’s tables below, the defined benefit pension plans costs represent those respective costs for their bargaining unit employees covered under the qualified plans that they sponsor, as well as amounts directly assigned to them related to their 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. In IPL’s and WPL’s tables below, the OPEB plans costs (credits) represent respective costs (credits) for their employees, as well as amounts directly assigned to them related to their current and former non-bargaining employees who are participants in the Corporate Services sponsored OPEB plan.

	Defined Benefit Pension Plans						OPEB Plans
Alliant Energy	2016			2015			2016			2015
Service cost		$3.2			$4.0			$1.3			$1.4
Interest cost	13.3			13.4			2.3			2.2
Expected return on plan assets	(16.4		)	(18.7		)	(1.5		)	(2.1		)
Amortization of prior service credit	(0.1		)	(0.1		)	(1.0		)	(2.8		)
Amortization of actuarial loss	9.3			8.8			1.2			1.2
Additional benefit costs	—			0.2			—			—
		$9.3			$7.6			$2.3			($0.1	)

	Defined Benefit Pension Plans						OPEB Plans
IPL	2016			2015			2016			2015
Service cost		$1.9			$2.2			$0.6			$0.6
Interest cost	6.1			6.2			1.0			0.9
Expected return on plan assets	(7.7		)	(8.9		)	(1.0		)	(1.4		)
Amortization of prior service credit	—			—			(0.7		)	(1.5		)
Amortization of actuarial loss	4.1			3.8			0.6			0.6
		$4.4			$3.3			$0.5			($0.8	)

	Defined Benefit Pension Plans						OPEB Plans
WPL	2016			2015			2016			2015
Service cost		$1.2			$1.4			$0.5			$0.6
Interest cost	5.6			5.6			0.9			0.9
Expected return on plan assets	(7.1		)	(8.1		)	(0.2		)	(0.4		)
Amortization of prior service cost (credit)	0.1			0.1			(0.2		)	(0.9		)
Amortization of actuarial loss	4.4			4.2			0.5			0.6
Additional benefit costs	—			0.2			—			—
		$4.2			$3.4			$1.5			$0.8

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’ contributions and include allocated costs associated with Corporate Services employees for IPL and WPL, were as follows (in millions):

	Alliant Energy				IPL				WPL
	2016		2015		2016		2015		2016		2015
401(k) costs		$6.2		$6.7		$3.1		$3.4		$2.8		$2.9

Recognized Compensation Expense And Income Tax Benefits

A summary of compensation expense, including amounts allocated to IPL and WPL, 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
	2016		2015		2016		2015		2016		2015
Compensation expense		$5.3		$3.2		$2.8		$1.7		$2.3		$1.4
Income tax benefits	2.2		1.3		1.1		0.7		0.9		0.6

Schedule Of Equity-based Compensation Plans Activity

Information related to fair values of nonvested performance shares and performance units at March 31, 2016, by year of grant, was as follows:

	Performance Shares									Performance Units
	2016 Grant			2015 Grant			2014 Grant			2016 Grant			2015 Grant			2014 Grant
Nonvested awards	33,161			45,403			49,719			11,959			17,209			19,235
Alliant Energy common stock closing price on March 31, 2016		$74.28			$74.28			$74.28			$74.28		N/A			N/A
Alliant Energy common stock closing price on grant date	N/A			N/A			N/A			N/A				$65.09			$53.77
Estimated payout percentage based on performance criteria	108		%	90		%	138		%	108		%	90		%	138		%
Fair values of each nonvested award		$80.22			$66.85			$102.51			$80.22			$58.58			$74.20

Performance Shares and Units [Member]

Defined Benefit Plan Disclosure [Line Items]

Schedule Of Equity-based Compensation Plans Activity

A summary of the performance shares and performance units activity, with amounts representing the target number of awards, was as follows:

	Performance Shares				Performance Units
	2016		2015		2016		2015
Nonvested awards, January 1	144,215		144,424		58,206		63,665
Granted	33,776		45,403		11,959		17,837
Vested	(49,093	)	(45,612	)	(21,380	)	(22,845	)
Forfeited	(615	)	—		(382	)	(93	)
Nonvested awards, March 31	128,283		144,215		48,403		58,564

Granted Awards - For the performance units granted in 2016, each performance unit’s value is based on the closing market price of one share of Alliant Energy’s common stock at the end of the performance period. For the performance units granted prior to 2016, each performance unit’s value is based on the closing market price of one share of Alliant Energy’s common stock on the grant date of the award.

Vested Awards - During the three months ended March 31, certain performance shares and performance units vested, resulting in payouts (a combination of cash and common stock for the performance shares and cash only for the performance units) as follows:

	Performance Shares						Performance Units
	2016			2015			2016			2015
	2013 Grant			2012 Grant			2013 Grant			2012 Grant
Performance awards vested	49,093			45,612			21,380			22,845
Percentage of target number of performance awards	165.0		%	167.5		%	165.0		%	167.5		%
Aggregate payout value (in millions)		$5.1			$5.1			$1.7			$1.6
Payout - cash (in millions)		$2.9			$3.2			$1.7			$1.6
Payout - common stock shares issued	11,204			10,975			N/A			N/A

Performance Contingent Restricted Stock [Member]

Defined Benefit Plan Disclosure [Line Items]

Schedule Of Equity-based Compensation Plans Activity

A summary of the performance contingent restricted stock activity was as follows:

	2016			2015
	Shares	Weighted Average Grant Date Fair Value		Shares		Weighted Average Grant Date Fair Value
Nonvested shares, January 1	95,122		$59.17	98,812			$50.69
Granted	—	—		45,403		65.09
Vested (a)	—	—		(49,093	)	47.58
Nonvested shares, March 31	95,122	59.17		95,122		59.17

(a) In 2015, 49,093 performance contingent restricted shares granted in 2013 vested because the specified performance criteria for such shares were met.

Performance Restricted Stock Unit [Member]

Defined Benefit Plan Disclosure [Line Items]

Schedule Of Equity-based Compensation Plans Activity

A summary of the performance restricted stock units activity, with amounts representing the target number of units, was as follows:

	2016
	Units		Weighted Average Grant Date Fair Value
Granted	33,776			$67.85
Forfeited	(615	)	67.80
Nonvested units, March 31	33,161		67.85

Performance Restricted Unit [Member]

Defined Benefit Plan Disclosure [Line Items]

Schedule Of Equity-based Compensation Plans Activity

A summary of the performance restricted units activity, with amounts representing the target number of units, was as follows:

	2016
Granted	11,959
Nonvested units, March 31	11,959

Key Employee Performance Restricted Unit [Member]

Defined Benefit Plan Disclosure [Line Items]

Schedule Of Equity-based Compensation Plans Activity

A summary of the key employee performance restricted units activity, with amounts representing the target number of units, was as follows:

	2016
	Units	Weighted Average Grant Date Fair Value
Granted	22,528		$67.80
Nonvested units, March 31	22,528	67.80

Restricted Stock Unit And Restricted Unit [Member]

Defined Benefit Plan Disclosure [Line Items]

Schedule Of Equity-based Compensation Plans Activity

A summary of the restricted stock units and restricted units activity was as follows:

	2016
	Restricted Stock Units		Restricted Units
Granted	28,952		10,251
Forfeited	(527	)	—
Nonvested units, March 31	28,425		10,251

Performance Contingent Cash Awards [Member]

Defined Benefit Plan Disclosure [Line Items]

Schedule Of Equity-based Compensation Plans Activity

A summary of the performance-contingent cash awards activity was as follows:

	2016		2015
Nonvested awards, January 1	81,876		78,930
Granted	—		41,105
Vested (a)	—		(37,332	)
Forfeited	(382	)	(469	)
Nonvested awards, March 31	81,494		82,234

(a) In 2015, 37,332 performance-contingent cash awards granted in 2013 vested, resulting in cash payouts valued at $2.4 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 sponsored defined benefit pension and OPEB plans for the three months ended March 31 are included in the tables below (in millions). In IPL’s and WPL’s tables below, the defined benefit pension plans costs represent those respective costs for their bargaining unit employees covered under the qualified plans that they sponsor, as well as amounts directly assigned to them related to their 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. In IPL’s and WPL’s tables below, the OPEB plans costs (credits) represent respective costs (credits) for their employees, as well as amounts directly assigned to them related to their current and former non-bargaining employees who are participants in the Corporate Services sponsored OPEB plan.

	Defined Benefit Pension Plans						OPEB Plans
Alliant Energy	2016			2015			2016			2015
Service cost		$3.2			$4.0			$1.3			$1.4
Interest cost	13.3			13.4			2.3			2.2
Expected return on plan assets	(16.4		)	(18.7		)	(1.5		)	(2.1		)
Amortization of prior service credit	(0.1		)	(0.1		)	(1.0		)	(2.8		)
Amortization of actuarial loss	9.3			8.8			1.2			1.2
Additional benefit costs	—			0.2			—			—
		$9.3			$7.6			$2.3			($0.1	)

	Defined Benefit Pension Plans						OPEB Plans
IPL	2016			2015			2016			2015
Service cost		$1.9			$2.2			$0.6			$0.6
Interest cost	6.1			6.2			1.0			0.9
Expected return on plan assets	(7.7		)	(8.9		)	(1.0		)	(1.4		)
Amortization of prior service credit	—			—			(0.7		)	(1.5		)
Amortization of actuarial loss	4.1			3.8			0.6			0.6
		$4.4			$3.3			$0.5			($0.8	)

	Defined Benefit Pension Plans						OPEB Plans
WPL	2016			2015			2016			2015
Service cost		$1.2			$1.4			$0.5			$0.6
Interest cost	5.6			5.6			0.9			0.9
Expected return on plan assets	(7.1		)	(8.1		)	(0.2		)	(0.4		)
Amortization of prior service cost (credit)	0.1			0.1			(0.2		)	(0.9		)
Amortization of actuarial loss	4.4			4.2			0.5			0.6
Additional benefit costs	—			0.2			—			—
		$4.2			$3.4			$1.5			$0.8

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’ contributions and include allocated costs associated with Corporate Services employees for IPL and WPL, were as follows (in millions):

	Alliant Energy				IPL				WPL
	2016		2015		2016		2015		2016		2015
401(k) costs		$6.2		$6.7		$3.1		$3.4		$2.8		$2.9

Recognized Compensation Expense And Income Tax Benefits

A summary of compensation expense, including amounts allocated to IPL and WPL, 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
	2016		2015		2016		2015		2016		2015
Compensation expense		$5.3		$3.2		$2.8		$1.7		$2.3		$1.4
Income tax benefits	2.2		1.3		1.1		0.7		0.9		0.6

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 sponsored defined benefit pension and OPEB plans for the three months ended March 31 are included in the tables below (in millions). In IPL’s and WPL’s tables below, the defined benefit pension plans costs represent those respective costs for their bargaining unit employees covered under the qualified plans that they sponsor, as well as amounts directly assigned to them related to their 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. In IPL’s and WPL’s tables below, the OPEB plans costs (credits) represent respective costs (credits) for their employees, as well as amounts directly assigned to them related to their current and former non-bargaining employees who are participants in the Corporate Services sponsored OPEB plan.

	Defined Benefit Pension Plans						OPEB Plans
Alliant Energy	2016			2015			2016			2015
Service cost		$3.2			$4.0			$1.3			$1.4
Interest cost	13.3			13.4			2.3			2.2
Expected return on plan assets	(16.4		)	(18.7		)	(1.5		)	(2.1		)
Amortization of prior service credit	(0.1		)	(0.1		)	(1.0		)	(2.8		)
Amortization of actuarial loss	9.3			8.8			1.2			1.2
Additional benefit costs	—			0.2			—			—
		$9.3			$7.6			$2.3			($0.1	)

	Defined Benefit Pension Plans						OPEB Plans
IPL	2016			2015			2016			2015
Service cost		$1.9			$2.2			$0.6			$0.6
Interest cost	6.1			6.2			1.0			0.9
Expected return on plan assets	(7.7		)	(8.9		)	(1.0		)	(1.4		)
Amortization of prior service credit	—			—			(0.7		)	(1.5		)
Amortization of actuarial loss	4.1			3.8			0.6			0.6
		$4.4			$3.3			$0.5			($0.8	)

	Defined Benefit Pension Plans						OPEB Plans
WPL	2016			2015			2016			2015
Service cost		$1.2			$1.4			$0.5			$0.6
Interest cost	5.6			5.6			0.9			0.9
Expected return on plan assets	(7.1		)	(8.1		)	(0.2		)	(0.4		)
Amortization of prior service cost (credit)	0.1			0.1			(0.2		)	(0.9		)
Amortization of actuarial loss	4.4			4.2			0.5			0.6
Additional benefit costs	—			0.2			—			—
		$4.2			$3.4			$1.5			$0.8

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’ contributions and include allocated costs associated with Corporate Services employees for IPL and WPL, were as follows (in millions):

	Alliant Energy				IPL				WPL
	2016		2015		2016		2015		2016		2015
401(k) costs		$6.2		$6.7		$3.1		$3.4		$2.8		$2.9

Recognized Compensation Expense And Income Tax Benefits

A summary of compensation expense, including amounts allocated to IPL and WPL, 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
	2016		2015		2016		2015		2016		2015
Compensation expense		$5.3		$3.2		$2.8		$1.7		$2.3		$1.4
Income tax benefits	2.2		1.3		1.1		0.7		0.9		0.6