Benefit Plans (Tables)

6 Months Ended

Jun. 30, 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 and six months ended June 30 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
	Three Months						Six Months						Three Months						Six Months
Alliant Energy	2016			2015			2016			2015			2016			2015			2016			2015
Service cost		$3.1			$3.9			$6.3			$7.9			$1.3			$1.4			$2.6			$2.8
Interest cost	13.2			13.4			26.5			26.8			2.4			2.3			4.7			4.5
Expected return on plan assets	(16.4		)	(18.8		)	(32.8		)	(37.5		)	(1.5		)	(2.1		)	(3.0		)	(4.2		)
Amortization of prior service credit	—			—			(0.1		)	(0.1		)	(1.1		)	(2.8		)	(2.1		)	(5.6		)
Amortization of actuarial loss	9.4			8.9			18.7			17.7			1.2			1.2			2.4			2.4
Additional benefit costs	—			0.1			—			0.3			—			—			—			—
		$9.3			$7.5			$18.6			$15.1			$2.3			$—			$4.6			($0.1	)

	Defined Benefit Pension Plans												OPEB Plans
	Three Months						Six Months						Three Months						Six Months
IPL	2016			2015			2016			2015			2016			2015			2016			2015
Service cost		$1.9			$2.2			$3.8			$4.4			$0.6			$0.6			$1.2			$1.2
Interest cost	6.2			6.3			12.3			12.5			0.9			1.0			1.9			1.9
Expected return on plan assets	(7.8		)	(9.0		)	(15.5		)	(17.9		)	(1.2		)	(1.4		)	(2.2		)	(2.8		)
Amortization of prior service credit	(0.1		)	(0.1		)	(0.1		)	(0.1		)	(0.6		)	(1.6		)	(1.3		)	(3.1		)
Amortization of actuarial loss	4.1			3.9			8.2			7.7			0.7			0.5			1.3			1.1
		$4.3			$3.3			$8.7			$6.6			$0.4			($0.9	)		$0.9			($1.7	)

	Defined Benefit Pension Plans												OPEB Plans
	Three Months						Six Months						Three Months						Six Months
WPL	2016			2015			2016			2015			2016			2015			2016			2015
Service cost		$1.2			$1.5			$2.4			$2.9			$0.5			$0.5			$1.0			$1.1
Interest cost	5.6			5.7			11.2			11.3			1.0			0.9			1.9			1.8
Expected return on plan assets	(7.1		)	(8.1		)	(14.2		)	(16.2		)	(0.2		)	(0.4		)	(0.4		)	(0.8		)
Amortization of prior service cost (credit)	—			—			0.1			0.1			(0.2		)	(0.8		)	(0.4		)	(1.7		)
Amortization of actuarial loss	4.4			4.2			8.8			8.4			0.4			0.5			0.9			1.1
Additional benefit costs	—			0.1			—			0.3			—			—			—			—
		$4.1			$3.4			$8.3			$6.8			$1.5			$0.7			$3.0			$1.5

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

	Alliant Energy								IPL								WPL
	Three Months				Six Months				Three Months				Six Months				Three Months				Six Months
	2016		2015		2016		2015		2016		2015		2016		2015		2016		2015		2016		2015
401(k) costs		$5.7		$5.6		$11.9		$12.3		$2.9		$2.9		$6.0		$6.3		$2.6		$2.6		$5.4		$5.5

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
	2016		2015		2016		2015		2016		2015		2016		2015		2016		2015		2016		2015
Compensation expense		$7.1		$2.3		$12.4		$5.5		$3.7		$1.2		$6.5		$2.9		$3.1		$1.0		$5.4		$2.4
Income tax benefits	2.9		0.9		5.1		2.2		1.6		0.5		2.7		1.2		1.3		0.4		2.2		1.0

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	288,430		288,848		116,412		127,330
Granted	68,585		90,806		23,918		35,674
Vested	(98,186	)	(91,224	)	(42,760	)	(45,690	)
Forfeited	(1,230	)	—		(4,139	)	(666	)
Nonvested awards, June 30	257,599		288,430		93,431		116,648

Granted Awards - For performance units granted in 2016, the final value is based on the closing market price of one share of Alliant Energy’s common stock at the end of the performance period. Compensation expense for performance shares and performance units is recorded ratably over the performance period based on the fair value of the awards at each reporting period.

Vested Awards - During the six months ended June 30, 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	98,186			91,224			42,760			45,690
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	22,408			21,950			N/A			N/A

Fair Value of Awards - Information related to fair values of nonvested performance shares and performance units at June 30, 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	67,355			90,806			99,438			22,768			33,268			37,395
Alliant Energy common stock closing price on June 30, 2016		$39.70			$39.70			$39.70			$39.70		N/A			N/A
Alliant Energy common stock closing price on grant date	N/A			N/A			N/A			N/A				$32.55			$26.89
Estimated payout percentage based on performance criteria	118		%	150		%	155		%	118		%	150		%	155		%
Fair values of each nonvested award		$46.85			$59.55			$61.54			$46.85			$48.82			$41.67

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	190,244		$29.59	197,624			$25.35
Granted	—	—		90,806		32.55
Vested (a)	—	—		(98,186	)	23.79
Nonvested shares, June 30	190,244	29.59		190,244		29.59

(a) In 2015, 98,186 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	68,585			$33.96
Forfeited	(1,230	)	33.90
Nonvested units, June 30	67,355		33.96

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	23,918
Forfeited	(1,150	)
Nonvested units, June 30	22,768

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
Granted	45,056
Forfeited	(1,238	)
Nonvested units, June 30	43,818

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	58,790		20,502
Forfeited	(1,054	)	(986	)
Nonvested units, June 30	57,736		19,516

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	163,752		157,860
Granted	—		82,210
Vested (a)	—		(74,664	)
Forfeited	(3,652	)	(1,418	)
Nonvested awards, June 30	160,100		163,988

(a) In 2015, 74,664 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 and six months ended June 30 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
	Three Months						Six Months						Three Months						Six Months
Alliant Energy	2016			2015			2016			2015			2016			2015			2016			2015
Service cost		$3.1			$3.9			$6.3			$7.9			$1.3			$1.4			$2.6			$2.8
Interest cost	13.2			13.4			26.5			26.8			2.4			2.3			4.7			4.5
Expected return on plan assets	(16.4		)	(18.8		)	(32.8		)	(37.5		)	(1.5		)	(2.1		)	(3.0		)	(4.2		)
Amortization of prior service credit	—			—			(0.1		)	(0.1		)	(1.1		)	(2.8		)	(2.1		)	(5.6		)
Amortization of actuarial loss	9.4			8.9			18.7			17.7			1.2			1.2			2.4			2.4
Additional benefit costs	—			0.1			—			0.3			—			—			—			—
		$9.3			$7.5			$18.6			$15.1			$2.3			$—			$4.6			($0.1	)

	Defined Benefit Pension Plans												OPEB Plans
	Three Months						Six Months						Three Months						Six Months
IPL	2016			2015			2016			2015			2016			2015			2016			2015
Service cost		$1.9			$2.2			$3.8			$4.4			$0.6			$0.6			$1.2			$1.2
Interest cost	6.2			6.3			12.3			12.5			0.9			1.0			1.9			1.9
Expected return on plan assets	(7.8		)	(9.0		)	(15.5		)	(17.9		)	(1.2		)	(1.4		)	(2.2		)	(2.8		)
Amortization of prior service credit	(0.1		)	(0.1		)	(0.1		)	(0.1		)	(0.6		)	(1.6		)	(1.3		)	(3.1		)
Amortization of actuarial loss	4.1			3.9			8.2			7.7			0.7			0.5			1.3			1.1
		$4.3			$3.3			$8.7			$6.6			$0.4			($0.9	)		$0.9			($1.7	)

	Defined Benefit Pension Plans												OPEB Plans
	Three Months						Six Months						Three Months						Six Months
WPL	2016			2015			2016			2015			2016			2015			2016			2015
Service cost		$1.2			$1.5			$2.4			$2.9			$0.5			$0.5			$1.0			$1.1
Interest cost	5.6			5.7			11.2			11.3			1.0			0.9			1.9			1.8
Expected return on plan assets	(7.1		)	(8.1		)	(14.2		)	(16.2		)	(0.2		)	(0.4		)	(0.4		)	(0.8		)
Amortization of prior service cost (credit)	—			—			0.1			0.1			(0.2		)	(0.8		)	(0.4		)	(1.7		)
Amortization of actuarial loss	4.4			4.2			8.8			8.4			0.4			0.5			0.9			1.1
Additional benefit costs	—			0.1			—			0.3			—			—			—			—
		$4.1			$3.4			$8.3			$6.8			$1.5			$0.7			$3.0			$1.5

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

	Alliant Energy								IPL								WPL
	Three Months				Six Months				Three Months				Six Months				Three Months				Six Months
	2016		2015		2016		2015		2016		2015		2016		2015		2016		2015		2016		2015
401(k) costs		$5.7		$5.6		$11.9		$12.3		$2.9		$2.9		$6.0		$6.3		$2.6		$2.6		$5.4		$5.5

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
	2016		2015		2016		2015		2016		2015		2016		2015		2016		2015		2016		2015
Compensation expense		$7.1		$2.3		$12.4		$5.5		$3.7		$1.2		$6.5		$2.9		$3.1		$1.0		$5.4		$2.4
Income tax benefits	2.9		0.9		5.1		2.2		1.6		0.5		2.7		1.2		1.3		0.4		2.2		1.0

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 and six months ended June 30 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
	Three Months						Six Months						Three Months						Six Months
Alliant Energy	2016			2015			2016			2015			2016			2015			2016			2015
Service cost		$3.1			$3.9			$6.3			$7.9			$1.3			$1.4			$2.6			$2.8
Interest cost	13.2			13.4			26.5			26.8			2.4			2.3			4.7			4.5
Expected return on plan assets	(16.4		)	(18.8		)	(32.8		)	(37.5		)	(1.5		)	(2.1		)	(3.0		)	(4.2		)
Amortization of prior service credit	—			—			(0.1		)	(0.1		)	(1.1		)	(2.8		)	(2.1		)	(5.6		)
Amortization of actuarial loss	9.4			8.9			18.7			17.7			1.2			1.2			2.4			2.4
Additional benefit costs	—			0.1			—			0.3			—			—			—			—
		$9.3			$7.5			$18.6			$15.1			$2.3			$—			$4.6			($0.1	)

	Defined Benefit Pension Plans												OPEB Plans
	Three Months						Six Months						Three Months						Six Months
IPL	2016			2015			2016			2015			2016			2015			2016			2015
Service cost		$1.9			$2.2			$3.8			$4.4			$0.6			$0.6			$1.2			$1.2
Interest cost	6.2			6.3			12.3			12.5			0.9			1.0			1.9			1.9
Expected return on plan assets	(7.8		)	(9.0		)	(15.5		)	(17.9		)	(1.2		)	(1.4		)	(2.2		)	(2.8		)
Amortization of prior service credit	(0.1		)	(0.1		)	(0.1		)	(0.1		)	(0.6		)	(1.6		)	(1.3		)	(3.1		)
Amortization of actuarial loss	4.1			3.9			8.2			7.7			0.7			0.5			1.3			1.1
		$4.3			$3.3			$8.7			$6.6			$0.4			($0.9	)		$0.9			($1.7	)

	Defined Benefit Pension Plans												OPEB Plans
	Three Months						Six Months						Three Months						Six Months
WPL	2016			2015			2016			2015			2016			2015			2016			2015
Service cost		$1.2			$1.5			$2.4			$2.9			$0.5			$0.5			$1.0			$1.1
Interest cost	5.6			5.7			11.2			11.3			1.0			0.9			1.9			1.8
Expected return on plan assets	(7.1		)	(8.1		)	(14.2		)	(16.2		)	(0.2		)	(0.4		)	(0.4		)	(0.8		)
Amortization of prior service cost (credit)	—			—			0.1			0.1			(0.2		)	(0.8		)	(0.4		)	(1.7		)
Amortization of actuarial loss	4.4			4.2			8.8			8.4			0.4			0.5			0.9			1.1
Additional benefit costs	—			0.1			—			0.3			—			—			—			—
		$4.1			$3.4			$8.3			$6.8			$1.5			$0.7			$3.0			$1.5

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

	Alliant Energy								IPL								WPL
	Three Months				Six Months				Three Months				Six Months				Three Months				Six Months
	2016		2015		2016		2015		2016		2015		2016		2015		2016		2015		2016		2015
401(k) costs		$5.7		$5.6		$11.9		$12.3		$2.9		$2.9		$6.0		$6.3		$2.6		$2.6		$5.4		$5.5

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
	2016		2015		2016		2015		2016		2015		2016		2015		2016		2015		2016		2015
Compensation expense		$7.1		$2.3		$12.4		$5.5		$3.7		$1.2		$6.5		$2.9		$3.1		$1.0		$5.4		$2.4
Income tax benefits	2.9		0.9		5.1		2.2		1.6		0.5		2.7		1.2		1.3		0.4		2.2		1.0