Benefit Plans (Tables)

12 Months Ended

Dec. 31, 2015

Defined Benefit Plan Disclosure [Line Items]

Assumptions Used To Measure Benefit Plans

The assumptions for defined benefit pension and OPEB plans at the measurement date of December 31 were as follows:

	Defined Benefit Pension Plans												OPEB Plans
Alliant Energy	2015				2014				2013				2015	2014	2013
Discount rate for benefit obligations	4.47%				4.18%				4.97%				4.30%	3.97%	4.59%
Discount rate for net periodic cost	4.18%				4.97%				4.11%				3.97%	4.59%	3.82%
Expected rate of return on plan assets	7.60%				7.60%				7.60%				6.20%	7.40%	7.40%
Rate of compensation increase	3.65	%	-	4.50%	3.50	%	-	4.50%	3.50	%	-	4.50%	N/A	N/A	3.50%
Medical cost trend on covered charges:
Initial trend rate (end of year)	N/A				N/A				N/A				7.25%	6.75%	7.00%
Ultimate trend rate	N/A				N/A				N/A				5.00%	5.00%	5.00%

	Qualified Defined Benefit Pension Plan			OPEB Plans
IPL	2015	2014	2013	2015	2014	2013
Discount rate for benefit obligations	4.50%	4.20%	5.05%	4.28%	3.94%	4.55%
Discount rate for net periodic cost	4.20%	5.05%	4.20%	3.94%	4.55%	3.76%
Expected rate of return on plan assets	7.60%	7.60%	7.60%	6.60%	7.60%	7.50%
Rate of compensation increase	3.65%	3.50%	3.50%	N/A	N/A	3.50%
Medical cost trend on covered charges:
Initial trend rate (end of year)	N/A	N/A	N/A	7.25%	6.75%	7.00%
Ultimate trend rate	N/A	N/A	N/A	5.00%	5.00%	5.00%

	Qualified Defined Benefit Pension Plan			OPEB Plans
WPL	2015	2014	2013	2015	2014	2013
Discount rate for benefit obligations	4.51%	4.20%	5.05%	4.28%	3.96%	4.56%
Discount rate for net periodic cost	4.20%	5.05%	4.20%	3.96%	4.56%	3.81%
Expected rate of return on plan assets	7.60%	7.60%	7.60%	4.60%	7.30%	7.20%
Rate of compensation increase	3.65%	3.50%	3.50%	N/A	N/A	3.50%
Medical cost trend on covered charges:
Initial trend rate (end of year)	N/A	N/A	N/A	7.25%	6.75%	7.00%
Ultimate trend rate	N/A	N/A	N/A	5.00%	5.00%	5.00%

Net Periodic Benefit Costs (Credits)

The components of net periodic benefit costs (credits) for sponsored defined benefit pension and OPEB plans 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.

Alliant Energy	Defined Benefit Pension Plans									OPEB Plans
	2015			2014			2013			2015			2014			2013
Service cost		$15.9			$13.1			$15.7			$5.5			$5.2			$6.3
Interest cost	53.6			54.1			49.0			9.1			9.5			8.5
Expected return on plan assets (a)	(75.0		)	(74.9		)	(74.0		)	(8.4		)	(8.3		)	(8.1		)
Amortization of prior service cost (credit) (b)	(0.2		)	—			0.2			(11.3		)	(11.9		)	(11.9		)
Amortization of actuarial loss (c)	35.4			19.5			36.2			4.8			2.4			4.9
Additional benefit costs (d)	0.5			—			9.0			—			—			—
		$30.2			$11.8			$36.1			($0.3	)		($3.1	)		($0.3	)

IPL	Defined Benefit Pension Plans									OPEB Plans
	2015			2014			2013			2015			2014			2013
Service cost		$8.8			$7.2			$8.6			$2.4			$2.4			$2.9
Interest cost	25.0			25.1			22.9			3.8			3.9			3.6
Expected return on plan assets (a)	(35.8		)	(35.7		)	(35.2		)	(5.7		)	(5.8		)	(5.6		)
Amortization of prior service cost (credit) (b)	(0.1		)	—			0.1			(6.1		)	(6.3		)	(6.3		)
Amortization of actuarial loss (c)	15.3			8.0			15.2			2.3			1.1			2.7
Additional benefit costs (d)	—			—			2.6			—			—			—
		$13.2			$4.6			$14.2			($3.3	)		($4.7	)		($2.7	)

WPL	Defined Benefit Pension Plans									OPEB Plans
	2015			2014			2013			2015			2014			2013
Service cost		$5.8			$4.9			$5.9			$2.1			$2.0			$2.5
Interest cost	22.6			22.6			20.7			3.7			3.8			3.4
Expected return on plan assets (a)	(32.4		)	(32.4		)	(31.9		)	(1.5		)	(1.3		)	(1.3		)
Amortization of prior service cost (credit) (b)	0.2			0.3			0.3			(3.5		)	(3.9		)	(3.9		)
Amortization of actuarial loss (c)	16.8			9.2			17.1			2.2			1.3			1.9
Additional benefit costs (d)	0.5			—			0.6			—			—			—
		$13.5			$4.6			$12.7			$3.0			$1.9			$2.6

(a) The expected return on plan assets is based on the expected rate of return on plan assets and the fair value approach to the market-related value of plan assets.

(b) Unrecognized prior service costs (credits) for the OPEB plans are amortized over the average future service period to full eligibility of the participants of each plan.

(c) Unrecognized net actuarial gains or losses in excess of 10% of the greater of the plans’ benefit obligations or assets are amortized over the average future service lives of plan participants, except for the Cash Balance Plan where gains or losses outside the 10% threshold are amortized over the time period the participants are expected to receive benefits.

(d) In 2013, Alliant Energy filed a stipulation agreement with the Western Wisconsin Court related to a class-action lawsuit against the Cash Balance Plan. As a result, Alliant Energy recognized $9.0 million of additional benefits costs in 2013 related to the agreement. IPL recognized $5.5 million ($2.6 million directly assigned and $2.9 million allocated by Corporate Services) and WPL recognized $2.8 million ($0.6 million directly assigned and $2.2 million allocated by Corporate Services) of additional benefits costs in 2013 related to the agreement.

Estimated Amortization From Regulatory Assets, Regulatory Liabilities And Accumulated Other Comprehensive Loss Into Net Periodic Benefit Cost

The estimated amortization from “Regulatory assets” and “Regulatory liabilities” on the balance sheets and AOCL on Alliant Energy’s balance sheet into net periodic benefit cost in 2016 is as follows (in millions):

	Alliant Energy						IPL						WPL
	Defined Benefit						Defined Benefit						Defined Benefit
	Pension Plans			OPEB Plans			Pension Plans			OPEB Plans			Pension Plans		OPEB Plans
Actuarial loss		$37.4			$4.8			$16.5			$2.6			$17.6		$1.8
Prior service cost (credit)	(0.3		)	(4.1		)	(0.2		)	(2.6		)	0.2		(0.9		)
		$37.1			$0.7			$16.3			$—			$17.8		$0.9

Funded Status Of Benefit Plans

A reconciliation of the funded status of Alliant Energy’s qualified and non-qualified defined benefit pension and OPEB plans to the amounts recognized on Alliant Energy’s balance sheets at December 31 was as follows (in millions):

	Defined Benefit
	Pension Plans						OPEB Plans
Alliant Energy	2015			2014			2015			2014
Change in benefit obligation:
Net benefit obligation at January 1		$1,301.5			$1,113.4			$231.1			$208.7
Service cost	15.9			13.1			5.5			5.2
Interest cost	53.6			54.1			9.1			9.5
Plan participants’ contributions	—			—			3.1			2.8
Plan amendments	—			—			(0.3		)	—
Additional benefit costs	0.5			—			—			—
Actuarial (gain) loss	(70.1		)	195.8			(9.4		)	22.3
Gross benefits paid	(95.1		)	(74.9		)	(17.7		)	(17.4		)
Net benefit obligation at December 31	1,206.3			1,301.5			221.4			231.1
Change in plan assets:
Fair value of plan assets at January 1	1,018.1			1,022.9			121.6			124.9
Actual return on plan assets	(30.2		)	66.4			(4.9		)	5.6
Employer contributions	2.2			3.7			4.8			5.7
Plan participants’ contributions	—			—			3.1			2.8
Gross benefits paid	(95.1		)	(74.9		)	(17.7		)	(17.4		)
Fair value of plan assets at December 31	895.0			1,018.1			106.9			121.6
Under funded status at December 31		($311.3	)		($283.4	)		($114.5	)		($109.5	)

	Defined Benefit
	Pension Plans						OPEB Plans
Alliant Energy	2015			2014			2015			2014
Amounts recognized on the balance sheets consist of:
Non-current assets		$—			$—			$3.0			$6.1
Other current liabilities	(2.6		)	(2.5		)	(6.2		)	(5.6		)
Pension and other benefit obligations	(308.7		)	(280.9		)	(111.3		)	(110.0		)
Net amounts recognized at December 31		($311.3	)		($283.4	)		($114.5	)		($109.5	)
Amounts recognized in Regulatory Assets and AOCL consist of (a):
Net actuarial loss		$533.1			$533.4			$59.8			$60.7
Prior service credit	(7.2		)	(7.4		)	(5.6		)	(16.7		)
		$525.9			$526.0			$54.2			$44.0

(a) Refer to Note 2 and Alliant Energy’s common equity statements for amounts recognized in “Regulatory assets” and “AOCL,” respectively, on Alliant Energy’s balance sheets.

Accumulated Benefit Obligations

Included in the following tables are accumulated benefit obligations, aggregate amounts applicable to defined benefit pension and OPEB plans with accumulated benefit obligations in excess of plan assets, as well as defined benefit pension plans with projected benefit obligations in excess of plan assets as of the December 31 measurement date (in millions):

	Defined Benefit
	Pension Plans				OPEB Plans
Alliant Energy	2015		2014		2015		2014
Accumulated benefit obligations		$1,166.0		$1,255.0		$221.4		$231.1
Plans with accumulated benefit obligations in excess of plan assets:
Accumulated benefit obligations	1,166.0		1,255.0		221.4		231.1
Fair value of plan assets	895.0		1,018.1		106.9		121.6
Plans with projected benefit obligations in excess of plan assets:
Projected benefit obligations	1,206.3		1,301.5		N/A		N/A
Fair value of plan assets	895.0		1,018.1		N/A		N/A

	Defined Benefit
	Pension Plans				OPEB Plans
IPL	2015		2014		2015		2014
Accumulated benefit obligations		$531.0		$575.5		$91.3		$96.4
Plans with accumulated benefit obligations in excess of plan assets:
Accumulated benefit obligations	531.0		575.5		91.3		96.4
Fair value of plan assets	422.7		484.7		69.2		78.7
Plans with projected benefit obligations in excess of plan assets:
Projected benefit obligations	556.1		603.1		N/A		N/A
Fair value of plan assets	422.7		484.7		N/A		N/A

	Defined Benefit
	Pension Plans				OPEB Plans
WPL	2015		2014		2015		2014
Accumulated benefit obligations		$493.8		$532.5		$89.7		$94.0
Plans with accumulated benefit obligations in excess of plan assets:
Accumulated benefit obligations	493.8		532.5		89.7		94.0
Fair value of plan assets	386.8		440.3		18.7		21.8
Plans with projected benefit obligations in excess of plan assets:
Projected benefit obligations	505.9		547.6		N/A		N/A
Fair value of plan assets	386.8		440.3		N/A		N/A

Regulatory Assets

In addition to the amounts recognized in regulatory assets in the above tables for IPL and WPL, regulatory assets were recognized for amounts associated with Corporate Services employees participating in other Alliant Energy sponsored benefit plans that were allocated to IPL and WPL at December 31 as follows (in millions):

	IPL				WPL
	2015		2014		2015		2014
Regulatory assets		$38.0		$38.2		$29.5		$28.0

Estimated Future Employer Contributions

Estimated funding for the qualified and non-qualified defined benefit pension and OPEB plans for 2016 is as follows (in millions):

	Alliant Energy		IPL		WPL
Defined benefit pension plans (a)		$2.6		$0.8		$0.1
OPEB plans	5.8		—		5.5

(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.

Expected Benefit Payments

Expected benefit payments for the qualified and non-qualified defined benefit plans, which reflect expected future service, as appropriate, are as follows (in millions):

Alliant Energy	2016		2017		2018		2019		2020		2021 - 2025
Defined benefit pension benefits		$69.5		$74.3		$72.8		$74.3		$78.7		$401.4
OPEB	17.8		18.1		18.2		18.3		18.2		86.9
		$87.3		$92.4		$91.0		$92.6		$96.9		$488.3

IPL	2016		2017		2018		2019		2020		2021 - 2025
Defined benefit pension benefits		$32.8		$34.1		$34.8		$34.6		$37.8		$190.8
OPEB	7.6		7.6		7.6		7.5		7.6		36.0
		$40.4		$41.7		$42.4		$42.1		$45.4		$226.8

WPL	2016		2017		2018		2019		2020		2021 - 2025
Defined benefit pension benefits		$29.1		$29.8		$30.7		$31.1		$32.2		$163.7
OPEB	7.5		7.8		7.8		7.8		7.6		34.7
		$36.6		$37.6		$38.5		$38.9		$39.8		$198.4

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 was as follows (in millions):

	Alliant Energy						IPL						WPL
	2015		2014		2013		2015		2014		2013		2015		2014		2013
Compensation expense		$10.7		$15.3		$12.0		$5.7		$8.3		$6.2		$4.7		$6.4		$5.2
Income tax benefits	4.4		6.2		4.8		2.4		3.4		2.5		1.9		2.6		2.1

Schedule Of Equity-based Compensation Plans Activity

Information related to fair values of nonvested performance shares and units at December 31, 2015, by year of grant, were 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			17,386			19,440			21,380
Alliant Energy common stock closing price on December 31, 2015		$62.45			$62.45			$62.45
Alliant Energy common stock closing price on grant date											$65.09			$53.77			$47.58
Estimated payout percentage based on performance criteria	80		%	125		%	165		%	80		%	125		%	165		%
Fair values of each nonvested award		$49.96			$78.06			$103.04			$52.07			$67.21			$78.51

Carrying Value And Fair Market Value Of The Deferred Compensation Obligations

At December 31, the carrying value of the deferred compensation obligation for the company stock accounts and the shares in the deferred compensation trust based on the historical value of the shares of Alliant Energy common stock contributed to the rabbi trust, and the fair market value of the shares held in the rabbi trust were as follows (in millions):

	2015		2014
Carrying value		$8.5		$8.9
Fair market value	13.4		15.9

Carrying Value Of Entity's Deferred Compensation Obligations Interest And Equity Accounts

At December 31, the carrying value of deferred compensation obligations for participants’ interest and equity accounts, which approximates fair market value, was as follows (in millions):

	Alliant Energy		IPL
	2015	2014	2015	2014
Carrying value	$18.3	$17.8	$5.0	$5.2

IPL [Member]

Defined Benefit Plan Disclosure [Line Items]

Assumptions Used To Measure Benefit Plans

The assumptions for defined benefit pension and OPEB plans at the measurement date of December 31 were as follows:

	Defined Benefit Pension Plans												OPEB Plans
Alliant Energy	2015				2014				2013				2015	2014	2013
Discount rate for benefit obligations	4.47%				4.18%				4.97%				4.30%	3.97%	4.59%
Discount rate for net periodic cost	4.18%				4.97%				4.11%				3.97%	4.59%	3.82%
Expected rate of return on plan assets	7.60%				7.60%				7.60%				6.20%	7.40%	7.40%
Rate of compensation increase	3.65	%	-	4.50%	3.50	%	-	4.50%	3.50	%	-	4.50%	N/A	N/A	3.50%
Medical cost trend on covered charges:
Initial trend rate (end of year)	N/A				N/A				N/A				7.25%	6.75%	7.00%
Ultimate trend rate	N/A				N/A				N/A				5.00%	5.00%	5.00%

	Qualified Defined Benefit Pension Plan			OPEB Plans
IPL	2015	2014	2013	2015	2014	2013
Discount rate for benefit obligations	4.50%	4.20%	5.05%	4.28%	3.94%	4.55%
Discount rate for net periodic cost	4.20%	5.05%	4.20%	3.94%	4.55%	3.76%
Expected rate of return on plan assets	7.60%	7.60%	7.60%	6.60%	7.60%	7.50%
Rate of compensation increase	3.65%	3.50%	3.50%	N/A	N/A	3.50%
Medical cost trend on covered charges:
Initial trend rate (end of year)	N/A	N/A	N/A	7.25%	6.75%	7.00%
Ultimate trend rate	N/A	N/A	N/A	5.00%	5.00%	5.00%

	Qualified Defined Benefit Pension Plan			OPEB Plans
WPL	2015	2014	2013	2015	2014	2013
Discount rate for benefit obligations	4.51%	4.20%	5.05%	4.28%	3.96%	4.56%
Discount rate for net periodic cost	4.20%	5.05%	4.20%	3.96%	4.56%	3.81%
Expected rate of return on plan assets	7.60%	7.60%	7.60%	4.60%	7.30%	7.20%
Rate of compensation increase	3.65%	3.50%	3.50%	N/A	N/A	3.50%
Medical cost trend on covered charges:
Initial trend rate (end of year)	N/A	N/A	N/A	7.25%	6.75%	7.00%
Ultimate trend rate	N/A	N/A	N/A	5.00%	5.00%	5.00%

Net Periodic Benefit Costs (Credits)

The components of net periodic benefit costs (credits) for sponsored defined benefit pension and OPEB plans 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.

Alliant Energy	Defined Benefit Pension Plans									OPEB Plans
	2015			2014			2013			2015			2014			2013
Service cost		$15.9			$13.1			$15.7			$5.5			$5.2			$6.3
Interest cost	53.6			54.1			49.0			9.1			9.5			8.5
Expected return on plan assets (a)	(75.0		)	(74.9		)	(74.0		)	(8.4		)	(8.3		)	(8.1		)
Amortization of prior service cost (credit) (b)	(0.2		)	—			0.2			(11.3		)	(11.9		)	(11.9		)
Amortization of actuarial loss (c)	35.4			19.5			36.2			4.8			2.4			4.9
Additional benefit costs (d)	0.5			—			9.0			—			—			—
		$30.2			$11.8			$36.1			($0.3	)		($3.1	)		($0.3	)

IPL	Defined Benefit Pension Plans									OPEB Plans
	2015			2014			2013			2015			2014			2013
Service cost		$8.8			$7.2			$8.6			$2.4			$2.4			$2.9
Interest cost	25.0			25.1			22.9			3.8			3.9			3.6
Expected return on plan assets (a)	(35.8		)	(35.7		)	(35.2		)	(5.7		)	(5.8		)	(5.6		)
Amortization of prior service cost (credit) (b)	(0.1		)	—			0.1			(6.1		)	(6.3		)	(6.3		)
Amortization of actuarial loss (c)	15.3			8.0			15.2			2.3			1.1			2.7
Additional benefit costs (d)	—			—			2.6			—			—			—
		$13.2			$4.6			$14.2			($3.3	)		($4.7	)		($2.7	)

WPL	Defined Benefit Pension Plans									OPEB Plans
	2015			2014			2013			2015			2014			2013
Service cost		$5.8			$4.9			$5.9			$2.1			$2.0			$2.5
Interest cost	22.6			22.6			20.7			3.7			3.8			3.4
Expected return on plan assets (a)	(32.4		)	(32.4		)	(31.9		)	(1.5		)	(1.3		)	(1.3		)
Amortization of prior service cost (credit) (b)	0.2			0.3			0.3			(3.5		)	(3.9		)	(3.9		)
Amortization of actuarial loss (c)	16.8			9.2			17.1			2.2			1.3			1.9
Additional benefit costs (d)	0.5			—			0.6			—			—			—
		$13.5			$4.6			$12.7			$3.0			$1.9			$2.6

(a) The expected return on plan assets is based on the expected rate of return on plan assets and the fair value approach to the market-related value of plan assets.

(b) Unrecognized prior service costs (credits) for the OPEB plans are amortized over the average future service period to full eligibility of the participants of each plan.

(c) Unrecognized net actuarial gains or losses in excess of 10% of the greater of the plans’ benefit obligations or assets are amortized over the average future service lives of plan participants, except for the Cash Balance Plan where gains or losses outside the 10% threshold are amortized over the time period the participants are expected to receive benefits.

(d) In 2013, Alliant Energy filed a stipulation agreement with the Western Wisconsin Court related to a class-action lawsuit against the Cash Balance Plan. As a result, Alliant Energy recognized $9.0 million of additional benefits costs in 2013 related to the agreement. IPL recognized $5.5 million ($2.6 million directly assigned and $2.9 million allocated by Corporate Services) and WPL recognized $2.8 million ($0.6 million directly assigned and $2.2 million allocated by Corporate Services) of additional benefits costs in 2013 related to the agreement.

Estimated Amortization From Regulatory Assets, Regulatory Liabilities And Accumulated Other Comprehensive Loss Into Net Periodic Benefit Cost

The estimated amortization from “Regulatory assets” and “Regulatory liabilities” on the balance sheets and AOCL on Alliant Energy’s balance sheet into net periodic benefit cost in 2016 is as follows (in millions):

	Alliant Energy						IPL						WPL
	Defined Benefit						Defined Benefit						Defined Benefit
	Pension Plans			OPEB Plans			Pension Plans			OPEB Plans			Pension Plans		OPEB Plans
Actuarial loss		$37.4			$4.8			$16.5			$2.6			$17.6		$1.8
Prior service cost (credit)	(0.3		)	(4.1		)	(0.2		)	(2.6		)	0.2		(0.9		)
		$37.1			$0.7			$16.3			$—			$17.8		$0.9

Funded Status Of Benefit Plans

A reconciliation of the funded status of IPL’s qualified and non-qualified defined benefit pension and OPEB plans to the amounts recognized on IPL’s balance sheets at December 31 was as follows (in millions):

	Defined Benefit
	Pension Plans						OPEB Plans
IPL	2015			2014			2015			2014
Change in benefit obligation:
Net benefit obligation at January 1		$603.1			$514.0			$96.4			$87.8
Service cost	8.8			7.2			2.4			2.4
Interest cost	25.0			25.1			3.8			3.9
Plan participants’ contributions	—			—			1.0			0.9
Plan amendments	—			—			(0.1		)	—
Actuarial (gain) loss	(32.3		)	91.4			(4.6		)	8.6
Gross benefits paid	(48.5		)	(34.6		)	(7.6		)	(7.2		)
Net benefit obligation at December 31	556.1			603.1			91.3			96.4
Change in plan assets:
Fair value of plan assets at January 1	484.7			485.9			78.7			81.2
Actual return on plan assets	(14.3		)	32.1			(3.1		)	3.6
Employer contributions	0.8			1.3			0.2			0.2
Plan participants’ contributions	—			—			1.0			0.9
Gross benefits paid	(48.5		)	(34.6		)	(7.6		)	(7.2		)
Fair value of plan assets at December 31	422.7			484.7			69.2			78.7
Under funded status at December 31		($133.4	)		($118.4	)		($22.1	)		($17.7	)

	Defined Benefit
	Pension Plans						OPEB Plans
IPL	2015			2014			2015			2014
Amounts recognized on the balance sheets consist of:
Non-current assets		$—			$—			$—			$1.2
Other current liabilities	(0.8		)	(0.8		)	—			—
Pension and other benefit obligations	(132.6		)	(117.6		)	(22.1		)	(18.9		)
Net amounts recognized at December 31		($133.4	)		($118.4	)		($22.1	)		($17.7	)
Amounts recognized in Regulatory Assets consist of (a):
Net actuarial loss		$235.5			$233.1			$29.8			$27.9
Prior service credit	(2.5		)	(2.6		)	(2.7		)	(8.7		)
		$233.0			$230.5			$27.1			$19.2

(a) Refer to Note 2 for amounts recognized in “Regulatory assets” on IPL’s balance sheets.

Accumulated Benefit Obligations

Included in the following tables are accumulated benefit obligations, aggregate amounts applicable to defined benefit pension and OPEB plans with accumulated benefit obligations in excess of plan assets, as well as defined benefit pension plans with projected benefit obligations in excess of plan assets as of the December 31 measurement date (in millions):

	Defined Benefit
	Pension Plans				OPEB Plans
Alliant Energy	2015		2014		2015		2014
Accumulated benefit obligations		$1,166.0		$1,255.0		$221.4		$231.1
Plans with accumulated benefit obligations in excess of plan assets:
Accumulated benefit obligations	1,166.0		1,255.0		221.4		231.1
Fair value of plan assets	895.0		1,018.1		106.9		121.6
Plans with projected benefit obligations in excess of plan assets:
Projected benefit obligations	1,206.3		1,301.5		N/A		N/A
Fair value of plan assets	895.0		1,018.1		N/A		N/A

	Defined Benefit
	Pension Plans				OPEB Plans
IPL	2015		2014		2015		2014
Accumulated benefit obligations		$531.0		$575.5		$91.3		$96.4
Plans with accumulated benefit obligations in excess of plan assets:
Accumulated benefit obligations	531.0		575.5		91.3		96.4
Fair value of plan assets	422.7		484.7		69.2		78.7
Plans with projected benefit obligations in excess of plan assets:
Projected benefit obligations	556.1		603.1		N/A		N/A
Fair value of plan assets	422.7		484.7		N/A		N/A

	Defined Benefit
	Pension Plans				OPEB Plans
WPL	2015		2014		2015		2014
Accumulated benefit obligations		$493.8		$532.5		$89.7		$94.0
Plans with accumulated benefit obligations in excess of plan assets:
Accumulated benefit obligations	493.8		532.5		89.7		94.0
Fair value of plan assets	386.8		440.3		18.7		21.8
Plans with projected benefit obligations in excess of plan assets:
Projected benefit obligations	505.9		547.6		N/A		N/A
Fair value of plan assets	386.8		440.3		N/A		N/A

Regulatory Assets

In addition to the amounts recognized in regulatory assets in the above tables for IPL and WPL, regulatory assets were recognized for amounts associated with Corporate Services employees participating in other Alliant Energy sponsored benefit plans that were allocated to IPL and WPL at December 31 as follows (in millions):

	IPL				WPL
	2015		2014		2015		2014
Regulatory assets		$38.0		$38.2		$29.5		$28.0

Estimated Future Employer Contributions

Estimated funding for the qualified and non-qualified defined benefit pension and OPEB plans for 2016 is as follows (in millions):

	Alliant Energy		IPL		WPL
Defined benefit pension plans (a)		$2.6		$0.8		$0.1
OPEB plans	5.8		—		5.5

(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.

Expected Benefit Payments

Expected benefit payments for the qualified and non-qualified defined benefit plans, which reflect expected future service, as appropriate, are as follows (in millions):

Alliant Energy	2016		2017		2018		2019		2020		2021 - 2025
Defined benefit pension benefits		$69.5		$74.3		$72.8		$74.3		$78.7		$401.4
OPEB	17.8		18.1		18.2		18.3		18.2		86.9
		$87.3		$92.4		$91.0		$92.6		$96.9		$488.3

IPL	2016		2017		2018		2019		2020		2021 - 2025
Defined benefit pension benefits		$32.8		$34.1		$34.8		$34.6		$37.8		$190.8
OPEB	7.6		7.6		7.6		7.5		7.6		36.0
		$40.4		$41.7		$42.4		$42.1		$45.4		$226.8

WPL	2016		2017		2018		2019		2020		2021 - 2025
Defined benefit pension benefits		$29.1		$29.8		$30.7		$31.1		$32.2		$163.7
OPEB	7.5		7.8		7.8		7.8		7.6		34.7
		$36.6		$37.6		$38.5		$38.9		$39.8		$198.4

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 was as follows (in millions):

	Alliant Energy						IPL						WPL
	2015		2014		2013		2015		2014		2013		2015		2014		2013
Compensation expense		$10.7		$15.3		$12.0		$5.7		$8.3		$6.2		$4.7		$6.4		$5.2
Income tax benefits	4.4		6.2		4.8		2.4		3.4		2.5		1.9		2.6		2.1

Carrying Value Of Entity's Deferred Compensation Obligations Interest And Equity Accounts

At December 31, the carrying value of deferred compensation obligations for participants’ interest and equity accounts, which approximates fair market value, was as follows (in millions):

	Alliant Energy		IPL
	2015	2014	2015	2014
Carrying value	$18.3	$17.8	$5.0	$5.2

WPL [Member]

Defined Benefit Plan Disclosure [Line Items]

Assumptions Used To Measure Benefit Plans

The assumptions for defined benefit pension and OPEB plans at the measurement date of December 31 were as follows:

	Defined Benefit Pension Plans												OPEB Plans
Alliant Energy	2015				2014				2013				2015	2014	2013
Discount rate for benefit obligations	4.47%				4.18%				4.97%				4.30%	3.97%	4.59%
Discount rate for net periodic cost	4.18%				4.97%				4.11%				3.97%	4.59%	3.82%
Expected rate of return on plan assets	7.60%				7.60%				7.60%				6.20%	7.40%	7.40%
Rate of compensation increase	3.65	%	-	4.50%	3.50	%	-	4.50%	3.50	%	-	4.50%	N/A	N/A	3.50%
Medical cost trend on covered charges:
Initial trend rate (end of year)	N/A				N/A				N/A				7.25%	6.75%	7.00%
Ultimate trend rate	N/A				N/A				N/A				5.00%	5.00%	5.00%

	Qualified Defined Benefit Pension Plan			OPEB Plans
IPL	2015	2014	2013	2015	2014	2013
Discount rate for benefit obligations	4.50%	4.20%	5.05%	4.28%	3.94%	4.55%
Discount rate for net periodic cost	4.20%	5.05%	4.20%	3.94%	4.55%	3.76%
Expected rate of return on plan assets	7.60%	7.60%	7.60%	6.60%	7.60%	7.50%
Rate of compensation increase	3.65%	3.50%	3.50%	N/A	N/A	3.50%
Medical cost trend on covered charges:
Initial trend rate (end of year)	N/A	N/A	N/A	7.25%	6.75%	7.00%
Ultimate trend rate	N/A	N/A	N/A	5.00%	5.00%	5.00%

	Qualified Defined Benefit Pension Plan			OPEB Plans
WPL	2015	2014	2013	2015	2014	2013
Discount rate for benefit obligations	4.51%	4.20%	5.05%	4.28%	3.96%	4.56%
Discount rate for net periodic cost	4.20%	5.05%	4.20%	3.96%	4.56%	3.81%
Expected rate of return on plan assets	7.60%	7.60%	7.60%	4.60%	7.30%	7.20%
Rate of compensation increase	3.65%	3.50%	3.50%	N/A	N/A	3.50%
Medical cost trend on covered charges:
Initial trend rate (end of year)	N/A	N/A	N/A	7.25%	6.75%	7.00%
Ultimate trend rate	N/A	N/A	N/A	5.00%	5.00%	5.00%

Net Periodic Benefit Costs (Credits)

The components of net periodic benefit costs (credits) for sponsored defined benefit pension and OPEB plans 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.

Alliant Energy	Defined Benefit Pension Plans									OPEB Plans
	2015			2014			2013			2015			2014			2013
Service cost		$15.9			$13.1			$15.7			$5.5			$5.2			$6.3
Interest cost	53.6			54.1			49.0			9.1			9.5			8.5
Expected return on plan assets (a)	(75.0		)	(74.9		)	(74.0		)	(8.4		)	(8.3		)	(8.1		)
Amortization of prior service cost (credit) (b)	(0.2		)	—			0.2			(11.3		)	(11.9		)	(11.9		)
Amortization of actuarial loss (c)	35.4			19.5			36.2			4.8			2.4			4.9
Additional benefit costs (d)	0.5			—			9.0			—			—			—
		$30.2			$11.8			$36.1			($0.3	)		($3.1	)		($0.3	)

IPL	Defined Benefit Pension Plans									OPEB Plans
	2015			2014			2013			2015			2014			2013
Service cost		$8.8			$7.2			$8.6			$2.4			$2.4			$2.9
Interest cost	25.0			25.1			22.9			3.8			3.9			3.6
Expected return on plan assets (a)	(35.8		)	(35.7		)	(35.2		)	(5.7		)	(5.8		)	(5.6		)
Amortization of prior service cost (credit) (b)	(0.1		)	—			0.1			(6.1		)	(6.3		)	(6.3		)
Amortization of actuarial loss (c)	15.3			8.0			15.2			2.3			1.1			2.7
Additional benefit costs (d)	—			—			2.6			—			—			—
		$13.2			$4.6			$14.2			($3.3	)		($4.7	)		($2.7	)

WPL	Defined Benefit Pension Plans									OPEB Plans
	2015			2014			2013			2015			2014			2013
Service cost		$5.8			$4.9			$5.9			$2.1			$2.0			$2.5
Interest cost	22.6			22.6			20.7			3.7			3.8			3.4
Expected return on plan assets (a)	(32.4		)	(32.4		)	(31.9		)	(1.5		)	(1.3		)	(1.3		)
Amortization of prior service cost (credit) (b)	0.2			0.3			0.3			(3.5		)	(3.9		)	(3.9		)
Amortization of actuarial loss (c)	16.8			9.2			17.1			2.2			1.3			1.9
Additional benefit costs (d)	0.5			—			0.6			—			—			—
		$13.5			$4.6			$12.7			$3.0			$1.9			$2.6

(a) The expected return on plan assets is based on the expected rate of return on plan assets and the fair value approach to the market-related value of plan assets.

(b) Unrecognized prior service costs (credits) for the OPEB plans are amortized over the average future service period to full eligibility of the participants of each plan.

(c) Unrecognized net actuarial gains or losses in excess of 10% of the greater of the plans’ benefit obligations or assets are amortized over the average future service lives of plan participants, except for the Cash Balance Plan where gains or losses outside the 10% threshold are amortized over the time period the participants are expected to receive benefits.

(d) In 2013, Alliant Energy filed a stipulation agreement with the Western Wisconsin Court related to a class-action lawsuit against the Cash Balance Plan. As a result, Alliant Energy recognized $9.0 million of additional benefits costs in 2013 related to the agreement. IPL recognized $5.5 million ($2.6 million directly assigned and $2.9 million allocated by Corporate Services) and WPL recognized $2.8 million ($0.6 million directly assigned and $2.2 million allocated by Corporate Services) of additional benefits costs in 2013 related to the agreement.

Estimated Amortization From Regulatory Assets, Regulatory Liabilities And Accumulated Other Comprehensive Loss Into Net Periodic Benefit Cost

The estimated amortization from “Regulatory assets” and “Regulatory liabilities” on the balance sheets and AOCL on Alliant Energy’s balance sheet into net periodic benefit cost in 2016 is as follows (in millions):

	Alliant Energy						IPL						WPL
	Defined Benefit						Defined Benefit						Defined Benefit
	Pension Plans			OPEB Plans			Pension Plans			OPEB Plans			Pension Plans		OPEB Plans
Actuarial loss		$37.4			$4.8			$16.5			$2.6			$17.6		$1.8
Prior service cost (credit)	(0.3		)	(4.1		)	(0.2		)	(2.6		)	0.2		(0.9		)
		$37.1			$0.7			$16.3			$—			$17.8		$0.9

Funded Status Of Benefit Plans

A reconciliation of the funded status of WPL’s qualified and non-qualified defined benefit pension and OPEB plans to the amounts recognized on WPL’s balance sheets at December 31 was as follows (in millions):

	Defined Benefit
	Pension Plans						OPEB Plans
WPL	2015			2014			2015			2014
Change in benefit obligation:
Net benefit obligation at January 1		$547.6			$460.8			$94.0			$85.6
Service cost	5.8			4.9			2.1			2.0
Interest cost	22.6			22.6			3.7			3.8
Plan participants’ contributions	—			—			1.6			1.3
Plan amendments	—			—			(0.2		)	—
Additional benefit costs	0.5			—			—			—
Actuarial (gain) loss	(30.0		)	86.7			(3.5		)	9.2
Gross benefits paid	(40.6		)	(27.4		)	(8.0		)	(7.9		)
Net benefit obligation at December 31	505.9			547.6			89.7			94.0
Change in plan assets:
Fair value of plan assets at January 1	440.3			438.8			21.8			21.7
Actual return on plan assets	(13.0		)	28.6			(1.1		)	1.2
Employer contributions	0.1			0.3			4.4			5.5
Plan participants’ contributions	—			—			1.6			1.3
Gross benefits paid	(40.6		)	(27.4		)	(8.0		)	(7.9		)
Fair value of plan assets at December 31	386.8			440.3			18.7			21.8
Under funded status at December 31		($119.1	)		($107.3	)		($71.0	)		($72.2	)

	Defined Benefit
	Pension Plans						OPEB Plans
WPL	2015			2014			2015			2014
Amounts recognized on the balance sheets consist of:
Non-current assets		$—			$—			$3.0			$4.9
Other current liabilities	(0.1		)	(0.1		)	(6.0		)	(5.5		)
Pension and other benefit obligations	(119.0		)	(107.2		)	(68.0		)	(71.6		)
Net amounts recognized at December 31		($119.1	)		($107.3	)		($71.0	)		($72.2	)
Amounts recognized in Regulatory Assets consist of (a):
Net actuarial loss		$232.1			$233.5			$23.3			$26.3
Prior service credit	(1.2		)	(1.0		)	(2.4		)	(5.6		)
		$230.9			$232.5			$20.9			$20.7

(a) Refer to Note 2 for amounts recognized in “Regulatory assets” on WPL’s balance sheets.

Accumulated Benefit Obligations

Included in the following tables are accumulated benefit obligations, aggregate amounts applicable to defined benefit pension and OPEB plans with accumulated benefit obligations in excess of plan assets, as well as defined benefit pension plans with projected benefit obligations in excess of plan assets as of the December 31 measurement date (in millions):

	Defined Benefit
	Pension Plans				OPEB Plans
Alliant Energy	2015		2014		2015		2014
Accumulated benefit obligations		$1,166.0		$1,255.0		$221.4		$231.1
Plans with accumulated benefit obligations in excess of plan assets:
Accumulated benefit obligations	1,166.0		1,255.0		221.4		231.1
Fair value of plan assets	895.0		1,018.1		106.9		121.6
Plans with projected benefit obligations in excess of plan assets:
Projected benefit obligations	1,206.3		1,301.5		N/A		N/A
Fair value of plan assets	895.0		1,018.1		N/A		N/A

	Defined Benefit
	Pension Plans				OPEB Plans
IPL	2015		2014		2015		2014
Accumulated benefit obligations		$531.0		$575.5		$91.3		$96.4
Plans with accumulated benefit obligations in excess of plan assets:
Accumulated benefit obligations	531.0		575.5		91.3		96.4
Fair value of plan assets	422.7		484.7		69.2		78.7
Plans with projected benefit obligations in excess of plan assets:
Projected benefit obligations	556.1		603.1		N/A		N/A
Fair value of plan assets	422.7		484.7		N/A		N/A

	Defined Benefit
	Pension Plans				OPEB Plans
WPL	2015		2014		2015		2014
Accumulated benefit obligations		$493.8		$532.5		$89.7		$94.0
Plans with accumulated benefit obligations in excess of plan assets:
Accumulated benefit obligations	493.8		532.5		89.7		94.0
Fair value of plan assets	386.8		440.3		18.7		21.8
Plans with projected benefit obligations in excess of plan assets:
Projected benefit obligations	505.9		547.6		N/A		N/A
Fair value of plan assets	386.8		440.3		N/A		N/A

Regulatory Assets

In addition to the amounts recognized in regulatory assets in the above tables for IPL and WPL, regulatory assets were recognized for amounts associated with Corporate Services employees participating in other Alliant Energy sponsored benefit plans that were allocated to IPL and WPL at December 31 as follows (in millions):

	IPL				WPL
	2015		2014		2015		2014
Regulatory assets		$38.0		$38.2		$29.5		$28.0

Estimated Future Employer Contributions

Estimated funding for the qualified and non-qualified defined benefit pension and OPEB plans for 2016 is as follows (in millions):

	Alliant Energy		IPL		WPL
Defined benefit pension plans (a)		$2.6		$0.8		$0.1
OPEB plans	5.8		—		5.5

(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.

Expected Benefit Payments

Expected benefit payments for the qualified and non-qualified defined benefit plans, which reflect expected future service, as appropriate, are as follows (in millions):

Alliant Energy	2016		2017		2018		2019		2020		2021 - 2025
Defined benefit pension benefits		$69.5		$74.3		$72.8		$74.3		$78.7		$401.4
OPEB	17.8		18.1		18.2		18.3		18.2		86.9
		$87.3		$92.4		$91.0		$92.6		$96.9		$488.3

IPL	2016		2017		2018		2019		2020		2021 - 2025
Defined benefit pension benefits		$32.8		$34.1		$34.8		$34.6		$37.8		$190.8
OPEB	7.6		7.6		7.6		7.5		7.6		36.0
		$40.4		$41.7		$42.4		$42.1		$45.4		$226.8

WPL	2016		2017		2018		2019		2020		2021 - 2025
Defined benefit pension benefits		$29.1		$29.8		$30.7		$31.1		$32.2		$163.7
OPEB	7.5		7.8		7.8		7.8		7.6		34.7
		$36.6		$37.6		$38.5		$38.9		$39.8		$198.4

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 was as follows (in millions):

	Alliant Energy						IPL						WPL
	2015		2014		2013		2015		2014		2013		2015		2014		2013
Compensation expense		$10.7		$15.3		$12.0		$5.7		$8.3		$6.2		$4.7		$6.4		$5.2
Income tax benefits	4.4		6.2		4.8		2.4		3.4		2.5		1.9		2.6		2.1

Pension Plans, Defined Benefit [Member]

Defined Benefit Plan Disclosure [Line Items]

Fair Value Of Plan Assets By Asset Category, Fair Value Hierarchy Level and Allocations

At December 31, the fair values of Alliant Energy’s qualified and non-qualified defined benefit pension plan assets by asset category and fair value hierarchy level were as follows (in millions):

	2015								2014
	Fair		Level		Level		Level		Fair			Level		Level		Level
	Value		1		2		3		Value			1		2		3
Cash and equivalents		$23.1		$—		$23.1		$—		$49.3			$—		$49.3		$—
Equity securities:
U.S. large cap core	100.4		100.4		—		—		137.2			137.2		—		—
U.S. large cap value	59.9		—		59.9		—		72.2			—		72.2		—
U.S. large cap growth	60.5		—		60.5		—		73.2			—		73.2		—
U.S. small cap value	14.2		—		14.2		—		15.2			—		15.2		—
U.S. small cap growth	16.0		16.0		—		—		15.9			15.9		—		—
International - developed markets	104.4		52.7		51.7		—		102.9			52.1		50.8		—
International - emerging markets	41.2		41.2		—		—		47.2			47.2		—		—
Global asset allocation securities	96.3		52.9		43.4		—		99.9			57.2		42.7		—
Risk parity allocation securities	94.0		—		94.0		—		102.5			—		102.5		—
Fixed income securities:
Corporate bonds	—		—		—		—		0.1			—		0.1		—
Fixed income funds	284.8		—		284.8		—		302.7			0.2		302.5		—
	894.8			$263.2		$631.6		$—	1,018.3				$309.8		$708.5		$—
Accrued investment income	0.2								0.1
Due to brokers, net (pending trades with brokers)	—								(0.3		)
Total pension plan assets		$895.0								$1,018.1

At December 31, 2015, the current target ranges and actual allocations for the defined benefit pension plan assets were as follows:

	Target Range				Actual
	Allocation				Allocation
Cash and equivalents	0	%	-	5%	2%
Equity securities:
U.S. large cap core	8	%	-	18%	11%
U.S. large cap value	2.5	%	-	12.5%	7%
U.S. large cap growth	2.5	%	-	12.5%	7%
U.S. small cap value	0	%	-	4%	1%
U.S. small cap growth	0	%	-	4%	2%
International - developed markets	7	%	-	19%	12%
International - emerging markets	0	%	-	10%	5%
Global asset allocation securities	5	%	-	15%	11%
Risk parity allocation securities	5	%	-	15%	10%
Fixed income securities	20	%	-	40%	32%

Pension Plans, Defined Benefit [Member] | IPL [Member]

Defined Benefit Plan Disclosure [Line Items]

Fair Value Of Plan Assets By Asset Category, Fair Value Hierarchy Level and Allocations

At December 31, 2015, the current target ranges and actual allocations for the defined benefit pension plan assets were as follows:

	Target Range				Actual
	Allocation				Allocation
Cash and equivalents	0	%	-	5%	2%
Equity securities:
U.S. large cap core	8	%	-	18%	11%
U.S. large cap value	2.5	%	-	12.5%	7%
U.S. large cap growth	2.5	%	-	12.5%	7%
U.S. small cap value	0	%	-	4%	1%
U.S. small cap growth	0	%	-	4%	2%
International - developed markets	7	%	-	19%	12%
International - emerging markets	0	%	-	10%	5%
Global asset allocation securities	5	%	-	15%	11%
Risk parity allocation securities	5	%	-	15%	10%
Fixed income securities	20	%	-	40%	32%

At December 31, the fair values of IPL’s qualified and non-qualified defined benefit pension plan assets by asset category and fair value hierarchy level were as follows (in millions):

	2015								2014
	Fair		Level		Level		Level		Fair			Level		Level		Level
	Value		1		2		3		Value			1		2		3
Cash and equivalents		$10.9		$—		$10.9		$—		$23.5			$—		$23.5		$—
Equity securities:
U.S. large cap core	47.4		47.4		—		—		65.3			65.3		—		—
U.S. large cap value	28.3		—		28.3		—		34.4			—		34.4		—
U.S. large cap growth	28.6		—		28.6		—		34.9			—		34.9		—
U.S. small cap value	6.7		—		6.7		—		7.2			—		7.2		—
U.S. small cap growth	7.5		7.5		—		—		7.6			7.6		—		—
International - developed markets	49.3		24.9		24.4		—		49.0			24.8		24.2		—
International - emerging markets	19.5		19.5		—		—		22.5			22.5		—		—
Global asset allocation securities	45.5		25.0		20.5		—		47.5			27.2		20.3		—
Risk parity allocation securities	44.4		—		44.4		—		48.8			—		48.8		—
Fixed income securities:
Fixed income funds	134.5		—		134.5		—		144.1			0.1		144.0		—
	422.6			$124.3		$298.3		$—	484.8				$147.5		$337.3		$—
Accrued investment income	0.1								0.1
Due to brokers, net (pending trades with brokers)	—								(0.2		)
Total pension plan assets		$422.7								$484.7

Pension Plans, Defined Benefit [Member] | WPL [Member]

Defined Benefit Plan Disclosure [Line Items]

Fair Value Of Plan Assets By Asset Category, Fair Value Hierarchy Level and Allocations

At December 31, the fair values of WPL’s qualified and non-qualified defined benefit pension plan assets by asset category and fair value hierarchy level were as follows (in millions):

	2015								2014
	Fair		Level		Level		Level		Fair			Level		Level		Level
	Value		1		2		3		Value			1		2		3
Cash and equivalents		$10.0		$—		$10.0		$—		$21.3			$—		$21.3		$—
Equity securities:
U.S. large cap core	43.4		43.4		—		—		59.3			59.3		—		—
U.S. large cap value	25.9		—		25.9		—		31.3			—		31.3		—
U.S. large cap growth	26.2		—		26.2		—		31.7			—		31.7		—
U.S. small cap value	6.1		—		6.1		—		6.6			—		6.6		—
U.S. small cap growth	6.9		6.9		—		—		6.9			6.9		—		—
International - developed markets	45.1		22.8		22.3		—		44.5			22.5		22.0		—
International - emerging markets	17.8		17.8		—		—		20.4			20.4		—		—
Global asset allocation securities	41.6		22.8		18.8		—		43.2			24.8		18.4		—
Risk parity allocation securities	40.6		—		40.6		—		44.3			—		44.3		—
Fixed income securities:
Fixed income funds	123.1		—		123.1		—		130.9			0.1		130.8		—
	386.7			$113.7		$273.0		$—	440.4				$134.0		$306.4		$—
Accrued investment income	0.1								—
Due to brokers, net (pending trades with brokers)	—								(0.1		)
Total pension plan assets		$386.8								$440.3

At December 31, 2015, the current target ranges and actual allocations for the defined benefit pension plan assets were as follows:

	Target Range				Actual
	Allocation				Allocation
Cash and equivalents	0	%	-	5%	2%
Equity securities:
U.S. large cap core	8	%	-	18%	11%
U.S. large cap value	2.5	%	-	12.5%	7%
U.S. large cap growth	2.5	%	-	12.5%	7%
U.S. small cap value	0	%	-	4%	1%
U.S. small cap growth	0	%	-	4%	2%
International - developed markets	7	%	-	19%	12%
International - emerging markets	0	%	-	10%	5%
Global asset allocation securities	5	%	-	15%	11%
Risk parity allocation securities	5	%	-	15%	10%
Fixed income securities	20	%	-	40%	32%

401(k) Savings Plan [Member]

Defined Benefit Plan Disclosure [Line Items]

Employees Participate In Defined Contribution Retirement Plans

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
	2015		2014		2013		2015		2014		2013		2015		2014		2013
401(k) costs		$24.9		$22.5		$19.2		$12.7		$11.1		$9.9		$11.2		$10.5		$8.5

401(k) Savings Plan [Member] | IPL [Member]

Defined Benefit Plan Disclosure [Line Items]

Employees Participate In Defined Contribution Retirement Plans

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
	2015		2014		2013		2015		2014		2013		2015		2014		2013
401(k) costs		$24.9		$22.5		$19.2		$12.7		$11.1		$9.9		$11.2		$10.5		$8.5

401(k) Savings Plan [Member] | WPL [Member]

Defined Benefit Plan Disclosure [Line Items]

Employees Participate In Defined Contribution Retirement Plans

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
	2015		2014		2013		2015		2014		2013		2015		2014		2013
401(k) costs		$24.9		$22.5		$19.2		$12.7		$11.1		$9.9		$11.2		$10.5		$8.5

Other Postretirement Benefits Plans [Member]

Defined Benefit Plan Disclosure [Line Items]

Fair Value Of Plan Assets By Asset Category, Fair Value Hierarchy Level and Allocations

At December 31, the fair values of Alliant Energy’s OPEB plan assets by asset category and fair value hierarchy level were as follows (in millions):

	2015								2014
	Fair		Level		Level		Level		Fair		Level		Level		Level
	Value		1		2		3		Value		1		2		3
Cash and equivalents		$3.6		$—		$3.6		$—		$3.7		$—		$3.7		$—
Equity securities:
U.S. blend	21.1		21.1		—		—		35.8		35.8		—		—
U.S. large cap core	0.9		0.9		—		—		2.9		2.9		—		—
U.S. large cap value	0.5		—		0.5		—		1.5		—		1.5		—
U.S. large cap growth	0.5		—		0.5		—		1.6		—		1.6		—
U.S. small cap value	0.1		—		0.1		—		0.3		—		0.3		—
U.S. small cap growth	0.1		0.1		—		—		0.4		0.4		—		—
International - blend	12.5		12.5		—		—		14.2		14.2		—		—
International - developed markets	1.0		0.5		0.5		—		2.2		1.1		1.1		—
International - emerging markets	0.4		0.4		—		—		1.0		1.0		—		—
Global asset allocation securities	16.4		16.0		0.4		—		30.3		29.4		0.9		—
Risk parity allocation securities	0.9		—		0.9		—		2.2		—		2.2		—
Fixed income securities:
Fixed income funds	48.9		46.3		2.6		—		25.5		19.0		6.5		—
Total OPEB plan assets		$106.9		$97.8		$9.1		$—		$121.6		$103.8		$17.8		$—

At December 31, 2015, the current target ranges and actual allocations for VEBA trusts with assets greater than $5 million and the WPL 401(h) assets were as follows:

	Target Range				Actual
	Allocation				Allocation
Cash and equivalents	0	%	-	15%	3%
Equity securities:
Domestic	0	%	-	45%	21%
International	0	%	-	21%	13%
Global asset allocation securities	5	%	-	40%	16%
Fixed income securities	10	%	-	70%	47%

Other Postretirement Benefits Plans [Member] | IPL [Member]

Defined Benefit Plan Disclosure [Line Items]

Fair Value Of Plan Assets By Asset Category, Fair Value Hierarchy Level and Allocations

At December 31, the fair values of IPL’s OPEB plan assets by asset category and fair value hierarchy level were as follows (in millions):

	2015								2014
	Fair		Level		Level		Level		Fair		Level		Level		Level
	Value		1		2		3		Value		1		2		3
Cash and equivalents		$0.9		$—		$0.9		$—		$1.4		$—		$1.4		$—
Equity securities:
U.S. blend	16.6		16.6		—		—		27.2		27.2		—		—
U.S. large cap core	0.1		0.1		—		—		0.5		0.5		—		—
U.S. large cap value	0.1		—		0.1		—		0.3		—		0.3		—
U.S. large cap growth	0.1		—		0.1		—		0.3		—		0.3		—
U.S. small cap value	—		—		—		—		0.1		—		0.1		—
U.S. small cap growth	—		—		—		—		0.1		0.1		—		—
International - blend	10.7		10.7		—		—		10.7		10.7		—		—
International - developed markets	0.1		0.1		—		—		0.4		0.2		0.2		—
International - emerging markets	—		—		—		—		0.2		0.2		—		—
Global asset allocation securities	6.9		6.9		—		—		21.6		21.5		0.1		—
Risk parity allocation securities	0.1		—		0.1		—		0.4		—		0.4		—
Fixed income securities:
Fixed income funds	33.6		33.3		0.3		—		15.5		14.3		1.2		—
Total OPEB plan assets		$69.2		$67.7		$1.5		$—		$78.7		$74.7		$4.0		$—

At December 31, 2015, the current target ranges and actual allocations for VEBA trusts with assets greater than $5 million and the WPL 401(h) assets were as follows:

	Target Range				Actual
	Allocation				Allocation
Cash and equivalents	0	%	-	15%	3%
Equity securities:
Domestic	0	%	-	45%	21%
International	0	%	-	21%	13%
Global asset allocation securities	5	%	-	40%	16%
Fixed income securities	10	%	-	70%	47%

Other Postretirement Benefits Plans [Member] | WPL [Member]

Defined Benefit Plan Disclosure [Line Items]

Fair Value Of Plan Assets By Asset Category, Fair Value Hierarchy Level and Allocations

At December 31, 2015, the current target ranges and actual allocations for VEBA trusts with assets greater than $5 million and the WPL 401(h) assets were as follows:

	Target Range				Actual
	Allocation				Allocation
Cash and equivalents	0	%	-	15%	3%
Equity securities:
Domestic	0	%	-	45%	21%
International	0	%	-	21%	13%
Global asset allocation securities	5	%	-	40%	16%
Fixed income securities	10	%	-	70%	47%

At December 31, the fair values of WPL’s OPEB plan assets by asset category and fair value hierarchy level were as follows (in millions):

	2015								2014
	Fair		Level		Level		Level		Fair		Level		Level		Level
	Value		1		2		3		Value		1		2		3
Cash and equivalents		$2.3		$—		$2.3		$—		$1.4		$—		$1.4		$—
Equity securities:
U.S. blend	—		—		—		—		3.6		3.6		—		—
U.S. large cap core	—		—		—		—		1.6		1.6		—		—
U.S. large cap value	—		—		—		—		0.8		—		0.8		—
U.S. large cap growth	—		—		—		—		0.8		—		0.8		—
U.S. small cap value	—		—		—		—		0.2		—		0.2		—
U.S. small cap growth	—		—		—		—		0.2		0.2		—		—
International - blend	—		—		—		—		1.4		1.4		—		—
International - developed markets	—		—		—		—		1.2		0.6		0.6		—
International - emerging markets	—		—		—		—		0.5		0.5		—		—
Global asset allocation securities	5.4		5.4		—		—		3.8		3.3		0.5		—
Risk parity allocation securities	—		—		—		—		1.1		—		1.1		—
Fixed income securities:
Fixed income funds	11.0		11.0		—		—		5.2		1.8		3.4		—
Total OPEB plan assets		$18.7		$16.4		$2.3		$—		$21.8		$13.0		$8.8		$—

Performance Shares [Member]

Defined Benefit Plan Disclosure [Line Items]

Schedule Of Equity-based Compensation Plans Activity

Performance shares can be paid out in shares of Alliant Energy’s common stock, cash or a combination of cash and stock. Each performance share’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. 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. A summary of the performance shares activity, with share amounts representing the target number of performance shares, was as follows:

	2015		2014		2013
Nonvested shares, January 1	144,424		139,940		145,277
Granted	45,403		51,221		49,093
Vested	(45,612	)	(45,235	)	(54,430	)
Forfeited	—		(1,502	)	—
Nonvested shares, December 31	144,215		144,424		139,940

Certain performance shares vested, resulting in payouts (a combination of cash and common stock) as follows:

	2015			2014			2013
	2012 Grant			2011 Grant			2010 Grant
Performance shares vested	45,612			45,235			54,430
Percentage of target number of performance shares	167.5		%	147.5		%	197.5		%
Aggregate payout value (in millions)		$5.1			$3.4			$4.8
Payout - cash (in millions)		$3.2			$2.9			$4.4
Payout - common stock shares issued	10,975			4,810			4,177

Performance Units [Member]

Defined Benefit Plan Disclosure [Line Items]

Schedule Of Equity-based Compensation Plans Activity

Performance units must be paid out in cash. Each performance unit’s value is based on the average 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. A summary of the performance unit activity, with amounts representing the target number of performance units, was as follows:

	2015		2014		2013
Nonvested units, January 1	63,665		65,912		64,969
Granted	17,837		20,422		22,201
Vested	(22,845	)	(20,751	)	(19,760	)
Forfeited	(451	)	(1,918	)	(1,498	)
Nonvested units, December 31	58,206		63,665		65,912

Certain performance units vested, resulting in cash payouts as follows:

	2015			2014			2013
	2012 Grant			2011 Grant			2010 Grant
Performance units vested	22,845			20,751			19,760
Percentage of target number of performance units	167.5		%	147.5		%	197.5		%
Payout value (in millions)		$1.6			$1.2			$1.3

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				2013
	Shares		Weighted Average Fair Value		Shares		Weighted Average Fair Value		Shares		Weighted Average Fair Value
Nonvested shares, January 1	98,812			$50.69	158,922			$42.71	211,651			$32.42
Granted	45,403		65.09		51,221		53.77		49,093		47.58
Vested (a)	(49,093	)	47.58		(90,847	)	40.91		—		—
Forfeited (b)	—		—		(20,484	)	39.85		(101,822	)	23.67
Nonvested shares, December 31	95,122		59.17		98,812		50.69		158,922		42.71

(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.

(b) In 2013, 101,822 performance-contingent restricted shares granted in 2009 were forfeited because the specified performance criteria for such shares were not met. The forfeitures during 2014 were primarily caused by retirements and terminations of participants.

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		2013
Nonvested awards, January 1	78,930		96,977		59,639
Granted	41,105		42,446		39,530
Vested (a)	(37,332	)	(55,517	)	—
Forfeited	(827	)	(4,976	)	(2,192	)
Nonvested awards, December 31	81,876		78,930		96,977

(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.