Benefit Plans (Tables)

6 Months Ended

Jun. 30, 2018

Defined Benefit Plan Disclosure [Line Items]

Defined Benefit Pension And Other Postretirement Benefits Plans

The components of net periodic benefit costs for sponsored defined benefit pension and OPEB plans for the three and six months ended June 30 are included in the tables below (in millions). The service cost component of net periodic benefit costs is included in “Other operation and maintenance” expenses in the income statements and all other components of net periodic benefit costs are included in “Other (income) and deductions” in the income statements. In IPL’s and WPL’s tables below, the defined benefit pension plan amounts represent those respective amounts 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 plan amounts represent respective amounts 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
	Three Months						Six Months						Three Months						Six Months
Alliant Energy	2018			2017			2018			2017			2018			2017			2018			2017
Service cost		$3.0			$3.1			$6.0			$6.2			$1.0			$1.3			$2.1			$2.5
Interest cost	11.7			12.8			23.4			25.6			1.9			2.1			3.8			4.3
Expected return on plan assets	(17.5		)	(16.4		)	(34.9		)	(32.8		)	(1.5		)	(1.6		)	(3.0		)	(3.1		)
Amortization of prior service credit	(0.1		)	(0.1		)	(0.3		)	(0.2		)	(0.1		)	—			(0.1		)	(0.1		)
Amortization of actuarial loss	8.8			9.4			17.6			18.8			0.9			0.9			1.7			1.9
		$5.9			$8.8			$11.8			$17.6			$2.2			$2.7			$4.5			$5.5

	Defined Benefit Pension Plans												OPEB Plans
	Three Months						Six Months						Three Months						Six Months
IPL	2018			2017			2018			2017			2018			2017			2018			2017
Service cost		$1.9			$1.9			$3.7			$3.7			$0.5			$0.6			$0.9			$1.1
Interest cost	5.4			5.8			10.7			11.7			0.8			0.9			1.6			1.8
Expected return on plan assets	(8.2		)	(7.7		)	(16.3		)	(15.4		)	(1.1		)	(1.1		)	(2.2		)	(2.2		)
Amortization of prior service credit	(0.1		)	(0.1		)	(0.1		)	(0.1		)	—			—			—			—
Amortization of actuarial loss	3.8			4.1			7.5			8.1			0.3			0.5			0.6			1.0
		$2.8			$4.0			$5.5			$8.0			$0.5			$0.9			$0.9			$1.7

	Defined Benefit Pension Plans												OPEB Plans
	Three Months						Six Months						Three Months						Six Months
WPL	2018			2017			2018			2017			2018			2017			2018			2017
Service cost		$1.1			$1.2			$2.2			$2.4			$0.4			$0.4			$0.8			$0.9
Interest cost	5.1			5.4			10.1			10.9			0.7			0.8			1.5			1.7
Expected return on plan assets	(7.6		)	(7.1		)	(15.2		)	(14.2		)	(0.1		)	(0.2		)	(0.3		)	(0.4		)
Amortization of prior service credit	(0.1		)	—			(0.1		)	—			(0.1		)	—			(0.1		)	(0.1		)
Amortization of actuarial loss	4.3			4.7			8.6			9.3			0.5			0.4			1.0			0.8
		$2.8			$4.2			$5.6			$8.4			$1.4			$1.4			$2.9			$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 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
	2018		2017		2018		2017		2018		2017		2018		2017		2018		2017		2018		2017
Compensation expense		$5.1		$1.6		$8.4		$4.8		$2.8		$0.9		$4.6		$2.6		$2.1		$0.6		$3.4		$2.0
Income tax benefits	1.5		0.6		2.4		1.9		0.9		0.4		1.4		1.1		0.5		0.3		0.9		0.8

Performance Shares and Performance 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 for the six months ended June 30, 2018, with amounts representing the target number of awards, was as follows:

	Performance Shares		Performance Units
Nonvested awards, January 1	223,511		71,737
Granted	74,163		19,840
Vested	(90,806	)	(31,910	)
Forfeited	(905	)	—
Nonvested awards, June 30	205,963		59,667

Vested Awards - During the six months ended June 30, 2018, certain performance shares and performance units that were granted in 2015 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
Performance awards vested	90,806			31,910
Percentage of target number of performance awards	137.5		%	137.5		%
Aggregate payout value (in millions)		$5.3			$1.4
Payout - cash (in millions)		$4.9			$1.4
Payout - common stock shares issued	5,078			N/A

Fair Value of Awards - At June 29, 2018, Alliant Energy’s common stock closing price was $42.32. Additional information related to fair values of nonvested performance shares and performance units at June 30, 2018, by year of grant, was as follows:

	Performance Shares									Performance Units
	2018 Grant			2017 Grant			2016 Grant			2018 Grant			2017 Grant			2016 Grant
Nonvested awards at target	73,258			65,350			67,355			19,840			18,600			21,227
Estimated payout percentage based on performance criteria	90		%	110		%	153		%	90		%	110		%	153		%
Fair values of each nonvested award		$38.09			$46.55			$64.75			$38.09			$46.55			$64.75

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 for the six months ended June 30, 2018, with amounts representing the target number of units, was as follows:

	Units		Weighted Average Grant Date Fair Value
Nonvested units, January 1	132,705			$36.50
Granted	74,163		38.60
Forfeited	(905	)	38.60
Nonvested units, June 30	205,963		37.25

Restricted Stock Unit [Member]

Defined Benefit Plan Disclosure [Line Items]

Schedule Of Equity-based Compensation Plans Activity

A summary of the restricted stock units activity for the six months ended June 30, 2018, was as follows:

Nonvested units, January 1	113,749
Granted	63,568
Forfeited	(775	)
Nonvested units, June 30	176,542

IPL [Member]

Defined Benefit Plan Disclosure [Line Items]

Defined Benefit Pension And Other Postretirement Benefits Plans

The components of net periodic benefit costs for sponsored defined benefit pension and OPEB plans for the three and six months ended June 30 are included in the tables below (in millions). The service cost component of net periodic benefit costs is included in “Other operation and maintenance” expenses in the income statements and all other components of net periodic benefit costs are included in “Other (income) and deductions” in the income statements. In IPL’s and WPL’s tables below, the defined benefit pension plan amounts represent those respective amounts 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 plan amounts represent respective amounts 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
	Three Months						Six Months						Three Months						Six Months
Alliant Energy	2018			2017			2018			2017			2018			2017			2018			2017
Service cost		$3.0			$3.1			$6.0			$6.2			$1.0			$1.3			$2.1			$2.5
Interest cost	11.7			12.8			23.4			25.6			1.9			2.1			3.8			4.3
Expected return on plan assets	(17.5		)	(16.4		)	(34.9		)	(32.8		)	(1.5		)	(1.6		)	(3.0		)	(3.1		)
Amortization of prior service credit	(0.1		)	(0.1		)	(0.3		)	(0.2		)	(0.1		)	—			(0.1		)	(0.1		)
Amortization of actuarial loss	8.8			9.4			17.6			18.8			0.9			0.9			1.7			1.9
		$5.9			$8.8			$11.8			$17.6			$2.2			$2.7			$4.5			$5.5

	Defined Benefit Pension Plans												OPEB Plans
	Three Months						Six Months						Three Months						Six Months
IPL	2018			2017			2018			2017			2018			2017			2018			2017
Service cost		$1.9			$1.9			$3.7			$3.7			$0.5			$0.6			$0.9			$1.1
Interest cost	5.4			5.8			10.7			11.7			0.8			0.9			1.6			1.8
Expected return on plan assets	(8.2		)	(7.7		)	(16.3		)	(15.4		)	(1.1		)	(1.1		)	(2.2		)	(2.2		)
Amortization of prior service credit	(0.1		)	(0.1		)	(0.1		)	(0.1		)	—			—			—			—
Amortization of actuarial loss	3.8			4.1			7.5			8.1			0.3			0.5			0.6			1.0
		$2.8			$4.0			$5.5			$8.0			$0.5			$0.9			$0.9			$1.7

	Defined Benefit Pension Plans												OPEB Plans
	Three Months						Six Months						Three Months						Six Months
WPL	2018			2017			2018			2017			2018			2017			2018			2017
Service cost		$1.1			$1.2			$2.2			$2.4			$0.4			$0.4			$0.8			$0.9
Interest cost	5.1			5.4			10.1			10.9			0.7			0.8			1.5			1.7
Expected return on plan assets	(7.6		)	(7.1		)	(15.2		)	(14.2		)	(0.1		)	(0.2		)	(0.3		)	(0.4		)
Amortization of prior service credit	(0.1		)	—			(0.1		)	—			(0.1		)	—			(0.1		)	(0.1		)
Amortization of actuarial loss	4.3			4.7			8.6			9.3			0.5			0.4			1.0			0.8
		$2.8			$4.2			$5.6			$8.4			$1.4			$1.4			$2.9			$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 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
	2018		2017		2018		2017		2018		2017		2018		2017		2018		2017		2018		2017
Compensation expense		$5.1		$1.6		$8.4		$4.8		$2.8		$0.9		$4.6		$2.6		$2.1		$0.6		$3.4		$2.0
Income tax benefits	1.5		0.6		2.4		1.9		0.9		0.4		1.4		1.1		0.5		0.3		0.9		0.8

WPL [Member]

Defined Benefit Plan Disclosure [Line Items]

Defined Benefit Pension And Other Postretirement Benefits Plans

The components of net periodic benefit costs for sponsored defined benefit pension and OPEB plans for the three and six months ended June 30 are included in the tables below (in millions). The service cost component of net periodic benefit costs is included in “Other operation and maintenance” expenses in the income statements and all other components of net periodic benefit costs are included in “Other (income) and deductions” in the income statements. In IPL’s and WPL’s tables below, the defined benefit pension plan amounts represent those respective amounts 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 plan amounts represent respective amounts 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
	Three Months						Six Months						Three Months						Six Months
Alliant Energy	2018			2017			2018			2017			2018			2017			2018			2017
Service cost		$3.0			$3.1			$6.0			$6.2			$1.0			$1.3			$2.1			$2.5
Interest cost	11.7			12.8			23.4			25.6			1.9			2.1			3.8			4.3
Expected return on plan assets	(17.5		)	(16.4		)	(34.9		)	(32.8		)	(1.5		)	(1.6		)	(3.0		)	(3.1		)
Amortization of prior service credit	(0.1		)	(0.1		)	(0.3		)	(0.2		)	(0.1		)	—			(0.1		)	(0.1		)
Amortization of actuarial loss	8.8			9.4			17.6			18.8			0.9			0.9			1.7			1.9
		$5.9			$8.8			$11.8			$17.6			$2.2			$2.7			$4.5			$5.5

	Defined Benefit Pension Plans												OPEB Plans
	Three Months						Six Months						Three Months						Six Months
IPL	2018			2017			2018			2017			2018			2017			2018			2017
Service cost		$1.9			$1.9			$3.7			$3.7			$0.5			$0.6			$0.9			$1.1
Interest cost	5.4			5.8			10.7			11.7			0.8			0.9			1.6			1.8
Expected return on plan assets	(8.2		)	(7.7		)	(16.3		)	(15.4		)	(1.1		)	(1.1		)	(2.2		)	(2.2		)
Amortization of prior service credit	(0.1		)	(0.1		)	(0.1		)	(0.1		)	—			—			—			—
Amortization of actuarial loss	3.8			4.1			7.5			8.1			0.3			0.5			0.6			1.0
		$2.8			$4.0			$5.5			$8.0			$0.5			$0.9			$0.9			$1.7

	Defined Benefit Pension Plans												OPEB Plans
	Three Months						Six Months						Three Months						Six Months
WPL	2018			2017			2018			2017			2018			2017			2018			2017
Service cost		$1.1			$1.2			$2.2			$2.4			$0.4			$0.4			$0.8			$0.9
Interest cost	5.1			5.4			10.1			10.9			0.7			0.8			1.5			1.7
Expected return on plan assets	(7.6		)	(7.1		)	(15.2		)	(14.2		)	(0.1		)	(0.2		)	(0.3		)	(0.4		)
Amortization of prior service credit	(0.1		)	—			(0.1		)	—			(0.1		)	—			(0.1		)	(0.1		)
Amortization of actuarial loss	4.3			4.7			8.6			9.3			0.5			0.4			1.0			0.8
		$2.8			$4.2			$5.6			$8.4			$1.4			$1.4			$2.9			$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 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
	2018		2017		2018		2017		2018		2017		2018		2017		2018		2017		2018		2017
Compensation expense		$5.1		$1.6		$8.4		$4.8		$2.8		$0.9		$4.6		$2.6		$2.1		$0.6		$3.4		$2.0
Income tax benefits	1.5		0.6		2.4		1.9		0.9		0.4		1.4		1.1		0.5		0.3		0.9		0.8