Benefit Plans (Tables)

6 Months Ended

Jun. 30, 2015

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 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 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 the “IPL” and “WPL” tables below, the OPEB plans costs (credits) represent costs (credits) for IPL and WPL employees, respectively, as well as amounts directly assigned to each of IPL and WPL 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	2015			2014			2015			2014			2015			2014			2015			2014
Service cost		$3.9			$3.3			$7.9			$6.6			$1.4			$1.3			$2.8			$2.6
Interest cost	13.4			13.5			26.8			27.0			2.3			2.3			4.5			4.7
Expected return on plan assets	(18.8		)	(18.8		)	(37.5		)	(37.5		)	(2.1		)	(2.0		)	(4.2		)	(4.1		)
Amortization of prior service credit	—			—			(0.1		)	—			(2.8		)	(2.9		)	(5.6		)	(5.9		)
Amortization of actuarial loss	8.9			5.0			17.7			9.8			1.2			0.6			2.4			1.2
Additional benefit costs	0.1			—			0.3			—			—			—			—			—
		$7.5			$3.0			$15.1			$5.9			$—			($0.7	)		($0.1	)		($1.5	)

	Defined Benefit Pension Plans												OPEB Plans
	Three Months						Six Months						Three Months						Six Months
IPL	2015			2014			2015			2014			2015			2014			2015			2014
Service cost		$2.2			$1.8			$4.4			$3.6			$0.6			$0.6			$1.2			$1.2
Interest cost	6.3			6.3			12.5			12.6			1.0			1.0			1.9			2.0
Expected return on plan assets	(9.0		)	(8.9		)	(17.9		)	(17.9		)	(1.4		)	(1.4		)	(2.8		)	(2.9		)
Amortization of prior service credit	(0.1		)	—			(0.1		)	—			(1.6		)	(1.5		)	(3.1		)	(3.1		)
Amortization of actuarial loss	3.9			2.0			7.7			4.0			0.5			0.2			1.1			0.5
		$3.3			$1.2			$6.6			$2.3			($0.9	)		($1.1	)		($1.7	)		($2.3	)

	Defined Benefit Pension Plans												OPEB Plans
	Three Months						Six Months						Three Months						Six Months
WPL	2015			2014			2015			2014			2015			2014			2015			2014
Service cost		$1.5			$1.2			$2.9			$2.4			$0.5			$0.5			$1.1			$1.0
Interest cost	5.7			5.6			11.3			11.3			0.9			0.9			1.8			1.9
Expected return on plan assets	(8.1		)	(8.1		)	(16.2		)	(16.2		)	(0.4		)	(0.3		)	(0.8		)	(0.6		)
Amortization of prior service cost (credit)	—			0.1			0.1			0.2			(0.8		)	(0.9		)	(1.7		)	(1.9		)
Amortization of actuarial loss	4.2			2.3			8.4			4.6			0.5			0.3			1.1			0.6
Additional benefit costs	0.1			—			0.3			—			—			—			—			—
		$3.4			$1.1			$6.8			$2.3			$0.7			$0.5			$1.5			$1.0

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, were as follows (in millions):

	Alliant Energy								IPL (a)								WPL (a)
	Three Months				Six Months				Three Months				Six Months				Three Months				Six Months
	2015		2014		2015		2014		2015		2014		2015		2014		2015		2014		2015		2014
401(k) costs		$5.6		$6.1		$12.3		$12.0		$2.9		$2.6		$6.3		$5.7		$2.6		$3.3		$5.5		$5.9

(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 (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
	2015		2014		2015		2014		2015		2014		2015		2014		2015		2014		2015		2014
Compensation expense		$2.3		$3.1		$5.5		$6.2		$1.2		$1.7		$2.9		$3.4		$1.0		$1.3		$2.4		$2.6
Income tax benefits	0.9		1.2		2.2		2.5		0.5		0.7		1.2		1.4		0.4		0.5		1.0		1.0

Schedule Of Equity-based Compensation Plans Activity

Information related to fair values of nonvested performance shares and units at June 30, 2015, by year of grant, was as follows:

	Performance Shares									Performance Units
	2015 Grant			2014 Grant			2013 Grant			2015 Grant			2014 Grant			2013 Grant
Nonvested awards	45,403			49,719			49,093			17,504			19,440			21,380
Alliant Energy common stock closing price on June 30, 2015		$57.72			$57.72			$57.72
Alliant Energy common stock closing price on grant date											$65.09			$53.77			$47.58
Estimated payout percentage based on performance criteria	100		%	133		%	180		%	100		%	133		%	180		%
Fair values of each nonvested award		$57.72			$76.77			$103.90			$65.09			$71.51			$85.64

Performance Shares [Member]

Defined Benefit Plan Disclosure [Line Items]

Schedule Of Equity-based Compensation Plans Activity

A summary of the performance shares activity was as follows:

	2015 (a)		2014 (a)
Nonvested shares, January 1	144,424		139,940
Granted	45,403		51,221
Vested	(45,612	)	(45,235	)
Forfeited	—		(1,502	)
Nonvested shares, June 30	144,215		144,424

(a) Share amounts represent the target number of performance shares.

During the six months ended June 30, certain performance shares vested, resulting in payouts (a combination of cash and common stock) as follows:

	2015			2014
	2012 Grant			2011 Grant
Performance shares vested	45,612			45,235
Percentage of target number of performance shares	167.5		%	147.5		%
Aggregate payout value (in millions)		$5.1			$3.4
Payout - cash (in millions)		$3.2			$2.9
Payout - common stock shares issued	10,975			4,810

Performance Units [Member]

Defined Benefit Plan Disclosure [Line Items]

Schedule Of Equity-based Compensation Plans Activity

A summary of the performance units activity was as follows:

	2015 (a)		2014 (a)
Nonvested units, January 1	63,665		65,912
Granted	17,837		20,422
Vested	(22,845	)	(20,751	)
Forfeited	(333	)	(761	)
Nonvested units, June 30	58,324		64,822

(a) Unit amounts represent the target number of performance units.

During the six months ended June 30, certain performance units vested, resulting in cash payouts as follows:

	2015			2014
	2012 Grant			2011 Grant
Performance units vested	22,845			20,751
Percentage of target number of performance units	167.5		%	147.5		%
Payout value (in millions)		$1.6			$1.2

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:

	2015				2014
	Shares		Weighted Average Fair Value		Shares		Weighted Average Fair Value
Nonvested shares, January 1	98,812			$50.69	158,922			$42.71
Granted	45,403		65.09		51,221		53.77
Vested (a)	(49,093	)	47.58		(90,847	)	40.91
Forfeited	—		—		(20,484	)	39.85
Nonvested shares, June 30	95,122		59.17		98,812		50.69

(a) In 2015, 49,093 performance contingent restricted shares granted in 2013 vested because the specified performance criteria for such shares were met. In 2014, 45,612 and 45,235 performance contingent restricted shares granted in 2012 and 2011, respectively, vested because the specified performance criteria for such shares were met.

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:

	2015		2014
Nonvested awards, January 1	78,930		96,977
Granted	41,105		42,446
Vested (a)	(37,332	)	(55,517	)
Forfeited	(709	)	(4,098	)
Nonvested awards, June 30	81,994		79,808

(a) In 2015, 37,332 performance contingent cash awards granted in 2013 vested, resulting in cash payouts valued at $2.4 million. In 2014, 34,766 and 20,751 performance contingent cash awards granted in 2012 and 2011 vested, resulting in cash payouts valued at $1.9 million and $1.1 million, respectively.

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 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 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 the “IPL” and “WPL” tables below, the OPEB plans costs (credits) represent costs (credits) for IPL and WPL employees, respectively, as well as amounts directly assigned to each of IPL and WPL 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	2015			2014			2015			2014			2015			2014			2015			2014
Service cost		$3.9			$3.3			$7.9			$6.6			$1.4			$1.3			$2.8			$2.6
Interest cost	13.4			13.5			26.8			27.0			2.3			2.3			4.5			4.7
Expected return on plan assets	(18.8		)	(18.8		)	(37.5		)	(37.5		)	(2.1		)	(2.0		)	(4.2		)	(4.1		)
Amortization of prior service credit	—			—			(0.1		)	—			(2.8		)	(2.9		)	(5.6		)	(5.9		)
Amortization of actuarial loss	8.9			5.0			17.7			9.8			1.2			0.6			2.4			1.2
Additional benefit costs	0.1			—			0.3			—			—			—			—			—
		$7.5			$3.0			$15.1			$5.9			$—			($0.7	)		($0.1	)		($1.5	)

	Defined Benefit Pension Plans												OPEB Plans
	Three Months						Six Months						Three Months						Six Months
IPL	2015			2014			2015			2014			2015			2014			2015			2014
Service cost		$2.2			$1.8			$4.4			$3.6			$0.6			$0.6			$1.2			$1.2
Interest cost	6.3			6.3			12.5			12.6			1.0			1.0			1.9			2.0
Expected return on plan assets	(9.0		)	(8.9		)	(17.9		)	(17.9		)	(1.4		)	(1.4		)	(2.8		)	(2.9		)
Amortization of prior service credit	(0.1		)	—			(0.1		)	—			(1.6		)	(1.5		)	(3.1		)	(3.1		)
Amortization of actuarial loss	3.9			2.0			7.7			4.0			0.5			0.2			1.1			0.5
		$3.3			$1.2			$6.6			$2.3			($0.9	)		($1.1	)		($1.7	)		($2.3	)

	Defined Benefit Pension Plans												OPEB Plans
	Three Months						Six Months						Three Months						Six Months
WPL	2015			2014			2015			2014			2015			2014			2015			2014
Service cost		$1.5			$1.2			$2.9			$2.4			$0.5			$0.5			$1.1			$1.0
Interest cost	5.7			5.6			11.3			11.3			0.9			0.9			1.8			1.9
Expected return on plan assets	(8.1		)	(8.1		)	(16.2		)	(16.2		)	(0.4		)	(0.3		)	(0.8		)	(0.6		)
Amortization of prior service cost (credit)	—			0.1			0.1			0.2			(0.8		)	(0.9		)	(1.7		)	(1.9		)
Amortization of actuarial loss	4.2			2.3			8.4			4.6			0.5			0.3			1.1			0.6
Additional benefit costs	0.1			—			0.3			—			—			—			—			—
		$3.4			$1.1			$6.8			$2.3			$0.7			$0.5			$1.5			$1.0

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, were as follows (in millions):

	Alliant Energy								IPL (a)								WPL (a)
	Three Months				Six Months				Three Months				Six Months				Three Months				Six Months
	2015		2014		2015		2014		2015		2014		2015		2014		2015		2014		2015		2014
401(k) costs		$5.6		$6.1		$12.3		$12.0		$2.9		$2.6		$6.3		$5.7		$2.6		$3.3		$5.5		$5.9

(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 (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
	2015		2014		2015		2014		2015		2014		2015		2014		2015		2014		2015		2014
Compensation expense		$2.3		$3.1		$5.5		$6.2		$1.2		$1.7		$2.9		$3.4		$1.0		$1.3		$2.4		$2.6
Income tax benefits	0.9		1.2		2.2		2.5		0.5		0.7		1.2		1.4		0.4		0.5		1.0		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 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 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 the “IPL” and “WPL” tables below, the OPEB plans costs (credits) represent costs (credits) for IPL and WPL employees, respectively, as well as amounts directly assigned to each of IPL and WPL 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	2015			2014			2015			2014			2015			2014			2015			2014
Service cost		$3.9			$3.3			$7.9			$6.6			$1.4			$1.3			$2.8			$2.6
Interest cost	13.4			13.5			26.8			27.0			2.3			2.3			4.5			4.7
Expected return on plan assets	(18.8		)	(18.8		)	(37.5		)	(37.5		)	(2.1		)	(2.0		)	(4.2		)	(4.1		)
Amortization of prior service credit	—			—			(0.1		)	—			(2.8		)	(2.9		)	(5.6		)	(5.9		)
Amortization of actuarial loss	8.9			5.0			17.7			9.8			1.2			0.6			2.4			1.2
Additional benefit costs	0.1			—			0.3			—			—			—			—			—
		$7.5			$3.0			$15.1			$5.9			$—			($0.7	)		($0.1	)		($1.5	)

	Defined Benefit Pension Plans												OPEB Plans
	Three Months						Six Months						Three Months						Six Months
IPL	2015			2014			2015			2014			2015			2014			2015			2014
Service cost		$2.2			$1.8			$4.4			$3.6			$0.6			$0.6			$1.2			$1.2
Interest cost	6.3			6.3			12.5			12.6			1.0			1.0			1.9			2.0
Expected return on plan assets	(9.0		)	(8.9		)	(17.9		)	(17.9		)	(1.4		)	(1.4		)	(2.8		)	(2.9		)
Amortization of prior service credit	(0.1		)	—			(0.1		)	—			(1.6		)	(1.5		)	(3.1		)	(3.1		)
Amortization of actuarial loss	3.9			2.0			7.7			4.0			0.5			0.2			1.1			0.5
		$3.3			$1.2			$6.6			$2.3			($0.9	)		($1.1	)		($1.7	)		($2.3	)

	Defined Benefit Pension Plans												OPEB Plans
	Three Months						Six Months						Three Months						Six Months
WPL	2015			2014			2015			2014			2015			2014			2015			2014
Service cost		$1.5			$1.2			$2.9			$2.4			$0.5			$0.5			$1.1			$1.0
Interest cost	5.7			5.6			11.3			11.3			0.9			0.9			1.8			1.9
Expected return on plan assets	(8.1		)	(8.1		)	(16.2		)	(16.2		)	(0.4		)	(0.3		)	(0.8		)	(0.6		)
Amortization of prior service cost (credit)	—			0.1			0.1			0.2			(0.8		)	(0.9		)	(1.7		)	(1.9		)
Amortization of actuarial loss	4.2			2.3			8.4			4.6			0.5			0.3			1.1			0.6
Additional benefit costs	0.1			—			0.3			—			—			—			—			—
		$3.4			$1.1			$6.8			$2.3			$0.7			$0.5			$1.5			$1.0

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, were as follows (in millions):

	Alliant Energy								IPL (a)								WPL (a)
	Three Months				Six Months				Three Months				Six Months				Three Months				Six Months
	2015		2014		2015		2014		2015		2014		2015		2014		2015		2014		2015		2014
401(k) costs		$5.6		$6.1		$12.3		$12.0		$2.9		$2.6		$6.3		$5.7		$2.6		$3.3		$5.5		$5.9

(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 (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
	2015		2014		2015		2014		2015		2014		2015		2014		2015		2014		2015		2014
Compensation expense		$2.3		$3.1		$5.5		$6.2		$1.2		$1.7		$2.9		$3.4		$1.0		$1.3		$2.4		$2.6
Income tax benefits	0.9		1.2		2.2		2.5		0.5		0.7		1.2		1.4		0.4		0.5		1.0		1.0