Benefit Plans (Tables)

12 Months Ended

Dec. 31, 2018

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	2018				2017				2016				2018	2017	2016
Discount rate for benefit obligations	4.34%				3.66%				4.19%				4.24%	3.53%	3.98%
Discount rate for net periodic cost	3.66%				4.19%				4.47%				3.53%	3.98%	4.30%
Expected rate of return on plan assets	7.60%				7.60%				7.60%				5.44%	5.80%	6.30%
Interest crediting rate for Alliant Energy Cash Balance Pension Plan	5.04%				4.64%				3.17%				N/A	N/A	N/A
Rate of compensation increase	3.65	%	-	4.50%	3.65	%	-	4.50%	3.65	%	-	4.50%	N/A	N/A	N/A
Medical cost trend on covered charges:
Initial trend rate (end of year)	N/A				N/A				N/A				6.50%	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	2018	2017	2016	2018	2017	2016
Discount rate for benefit obligations	4.35%	3.68%	4.22%	4.23%	3.51%	3.95%
Discount rate for net periodic cost	3.68%	4.22%	4.50%	3.51%	3.95%	4.28%
Expected rate of return on plan assets	7.60%	7.60%	7.60%	5.60%	6.20%	6.60%
Rate of compensation increase	3.65%	3.65%	3.65%	N/A	N/A	N/A
Medical cost trend on covered charges:
Initial trend rate (end of year)	N/A	N/A	N/A	6.50%	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	2018	2017	2016	2018	2017	2016
Discount rate for benefit obligations	4.35%	3.69%	4.23%	4.23%	3.51%	3.96%
Discount rate for net periodic cost	3.69%	4.23%	4.51%	3.51%	3.96%	4.28%
Expected rate of return on plan assets	7.60%	7.60%	7.60%	3.84%	3.50%	4.70%
Rate of compensation increase	3.65%	3.65%	3.65%	N/A	N/A	N/A
Medical cost trend on covered charges:
Initial trend rate (end of year)	N/A	N/A	N/A	6.50%	6.75%	7.00%
Ultimate trend rate	N/A	N/A	N/A	5.00%	5.00%	5.00%

Net Periodic Benefit Costs

The components of net periodic benefit costs for sponsored defined benefit pension and OPEB plans are included in the tables below (in millions). The service cost component of net periodic benefit costs is included in “Other operation and maintenance” expenses in the income statements and all other components of net periodic benefit costs are included in “Other (income) and deductions” in the income statements.

Alliant Energy	Defined Benefit Pension Plans									OPEB Plans
	2018			2017			2016			2018			2017			2016
Service cost		$12.1			$12.5			$12.6			$4.2			$5.0			$5.3
Interest cost	46.8			51.0			53.0			7.7			8.6			9.4
Expected return on plan assets (a)	(69.7		)	(65.5		)	(65.5		)	(6.0		)	(6.1		)	(6.1		)
Amortization of prior service credit (b)	(0.7		)	(0.4		)	(0.3		)	(0.2		)	(0.2		)	(4.1		)
Amortization of actuarial loss (c)	35.2			37.6			37.4			3.4			3.8			4.7
Settlement losses (d)	—			0.9			—			—			—			—
		$23.7			$36.1			$37.2			$9.1			$11.1			$9.2

IPL	Defined Benefit Pension Plans									OPEB Plans
	2018			2017			2016			2018			2017			2016
Service cost		$7.4			$7.3			$7.5			$1.7			$2.1			$2.3
Interest cost	21.4			23.5			24.5			3.1			3.5			3.8
Expected return on plan assets (a)	(32.6		)	(30.8		)	(30.9		)	(4.4		)	(4.3		)	(4.3		)
Amortization of prior service credit (b)	(0.2		)	(0.2		)	(0.2		)	—			—			(2.6		)
Amortization of actuarial loss (c)	14.9			16.1			16.5			1.3			2.0			2.6
		$10.9			$15.9			$17.4			$1.7			$3.3			$1.8

WPL	Defined Benefit Pension Plans									OPEB Plans
	2018			2017			2016			2018			2017			2016
Service cost		$4.4			$4.9			$4.9			$1.6			$1.9			$2.0
Interest cost	20.2			21.8			22.3			3.1			3.4			3.8
Expected return on plan assets (a)	(30.4		)	(28.5		)	(28.3		)	(0.6		)	(0.8		)	(0.8		)
Amortization of prior service cost (credit) (b)	(0.1		)	0.1			0.2			(0.2		)	(0.2		)	(0.9		)
Amortization of actuarial loss (c)	17.2			18.5			17.6			2.0			1.6			1.8
		$11.3			$16.8			$16.7			$5.9			$5.9			$5.9

(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 Alliant Energy Cash Balance Pension Plan where gains or losses outside the 10% threshold are amortized over the time period the participants are expected to receive benefits.

(d) Settlement losses related to payments made to retired executives of Alliant Energy.

Funded Status Of Benefit Plans

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

	Defined Benefit Pension Plans						OPEB Plans
Alliant Energy	2018			2017			2018			2017
Change in benefit obligation:
Net benefit obligation at January 1		$1,303.1			$1,244.3			$222.3			$220.1
Service cost	12.1			12.5			4.2			5.0
Interest cost	46.8			51.0			7.7			8.6
Plan participants’ contributions	—			—			3.1			2.9
Actuarial (gain) loss	(96.2		)	83.6			(8.2		)	5.4
Gross benefits paid	(90.8		)	(88.3		)	(23.0		)	(19.7		)
Net benefit obligation at December 31	1,175.0			1,303.1			206.1			222.3
Change in plan assets:
Fair value of plan assets at January 1	950.7			895.7			111.1			105.8
Actual return on plan assets	(57.8		)	136.7			(2.6		)	12.9
Employer contributions	6.5			6.6			10.5			9.2
Plan participants’ contributions	—			—			3.1			2.9
Gross benefits paid	(90.8		)	(88.3		)	(23.0		)	(19.7		)
Fair value of plan assets at December 31	808.6			950.7			99.1			111.1
Under funded status at December 31		($366.4	)		($352.4	)		($107.0	)		($111.2	)

	Defined Benefit Pension Plans						OPEB Plans
Alliant Energy	2018			2017			2018			2017
Amounts recognized on the balance sheets consist of:
Non-current assets		$—			$—			$7.5			$8.8
Current liabilities	(2.3		)	(2.2		)	(9.6		)	(9.1		)
Pension and other benefit obligations	(364.1		)	(350.2		)	(104.9		)	(110.9		)
Net amounts recognized at December 31		($366.4	)		($352.4	)		($107.0	)		($111.2	)
Amounts recognized in Regulatory Assets consist of:
Net actuarial loss		$505.2			$509.1			$44.5			$47.4
Prior service credit	(5.8		)	(6.5		)	(1.1		)	(1.3		)
		$499.4			$502.6			$43.4			$46.1

	Defined Benefit Pension Plans						OPEB Plans
IPL	2018			2017			2018			2017
Change in benefit obligation:
Net benefit obligation at January 1		$592.9			$570.4			$89.4			$90.1
Service cost	7.4			7.3			1.7			2.1
Interest cost	21.4			23.5			3.1			3.5
Plan participants’ contributions	—			—			1.0			1.0
Actuarial (gain) loss	(44.4		)	34.9			(4.3		)	(0.1		)
Gross benefits paid	(43.4		)	(43.2		)	(8.4		)	(7.2		)
Net benefit obligation at December 31	533.9			592.9			82.5			89.4
Change in plan assets:
Fair value of plan assets at January 1	443.7			422.0			72.9			68.2
Actual return on plan assets	(26.8		)	64.3			(1.4		)	8.9
Employer contributions	4.3			0.6			2.6			2.0
Plan participants’ contributions	—			—			1.0			1.0
Gross benefits paid	(43.4		)	(43.2		)	(8.4		)	(7.2		)
Fair value of plan assets at December 31	377.8			443.7			66.7			72.9
Under funded status at December 31		($156.1	)		($149.2	)		($15.8	)		($16.5	)

	Defined Benefit Pension Plans						OPEB Plans
IPL	2018			2017			2018			2017
Amounts recognized on the balance sheets consist of:
Non-current assets		$—			$—			$4.7			$5.9
Current liabilities	(0.6		)	(0.5		)	(1.9		)	(2.0		)
Pension and other benefit obligations	(155.5		)	(148.7		)	(18.6		)	(20.4		)
Net amounts recognized at December 31		($156.1	)		($149.2	)		($15.8	)		($16.5	)
Amounts recognized in Regulatory Assets consist of:
Net actuarial loss		$218.8			$218.9			$18.8			$18.7
Prior service credit	(1.8		)	(2.1		)	—			—
		$217.0			$216.8			$18.8			$18.7

	Defined Benefit Pension Plans						OPEB Plans
WPL	2018			2017			2018			2017
Change in benefit obligation:
Net benefit obligation at January 1		$559.8			$529.2			$90.4			$88.9
Service cost	4.4			4.9			1.6			1.9
Interest cost	20.2			21.8			3.1			3.4
Plan participants’ contributions	—			—			1.4			1.4
Actuarial (gain) loss	(40.0		)	38.3			(2.5		)	4.1
Gross benefits paid	(37.8		)	(34.4		)	(10.8		)	(9.3		)
Net benefit obligation at December 31	506.6			559.8			83.2			90.4
Change in plan assets:
Fair value of plan assets at January 1	415.0			389.7			18.7			18.6
Actual return on plan assets	(25.1		)	59.6			(0.1		)	1.2
Employer contributions	0.1			0.1			7.5			6.8
Plan participants’ contributions	—			—			1.4			1.4
Gross benefits paid	(37.8		)	(34.4		)	(10.8		)	(9.3		)
Fair value of plan assets at December 31	352.2			415.0			16.7			18.7
Under funded status at December 31		($154.4	)		($144.8	)		($66.5	)		($71.7	)

	Defined Benefit Pension Plans						OPEB Plans
WPL	2018			2017			2018			2017
Amounts recognized on the balance sheets consist of:
Non-current assets		$—			$—			$2.8			$2.9
Current liabilities	(0.1		)	(0.1		)	(7.4		)	(6.8		)
Pension and other benefit obligations	(154.3		)	(144.7		)	(61.9		)	(67.8		)
Net amounts recognized at December 31		($154.4	)		($144.8	)		($66.5	)		($71.7	)
Amounts recognized in Regulatory Assets consist of:
Net actuarial loss		$223.0			$224.7			$19.9			$23.6
Prior service credit	(1.3		)	(1.5		)	(1.1		)	(1.3		)
		$221.7			$223.2			$18.8			$22.3

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	2018		2017		2018		2017
Accumulated benefit obligations		$1,139.9		$1,269.0		$206.1		$222.3
Plans with accumulated benefit obligations in excess of plan assets:
Accumulated benefit obligations	1,139.9		1,269.0		206.1		222.3
Fair value of plan assets	808.6		950.7		99.1		111.1
Plans with projected benefit obligations in excess of plan assets:
Projected benefit obligations	1,175.0		1,303.1		N/A		N/A
Fair value of plan assets	808.6		950.7		N/A		N/A

	Defined Benefit Pension Plans				OPEB Plans
IPL	2018		2017		2018		2017
Accumulated benefit obligations		$514.3		$573.1		$82.5		$89.4
Plans with accumulated benefit obligations in excess of plan assets:
Accumulated benefit obligations	514.3		573.1		82.5		89.4
Fair value of plan assets	377.8		443.7		66.7		72.9
Plans with projected benefit obligations in excess of plan assets:
Projected benefit obligations	533.9		592.9		N/A		N/A
Fair value of plan assets	377.8		443.7		N/A		N/A

	Defined Benefit Pension Plans				OPEB Plans
WPL	2018		2017		2018		2017
Accumulated benefit obligations		$494.8		$548.1		$83.2		$90.4
Plans with accumulated benefit obligations in excess of plan assets:
Accumulated benefit obligations	494.8		548.1		83.2		90.4
Fair value of plan assets	352.2		415.0		16.7		18.7
Plans with projected benefit obligations in excess of plan assets:
Projected benefit obligations	506.6		559.8		N/A		N/A
Fair value of plan assets	352.2		415.0		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
	2018		2017		2018		2017
Regulatory assets		$38.2		$38.9		$27.7		$28.1

Estimated Future Employer Contributions

Estimated funding for the qualified and non-qualified defined benefit pension and OPEB plans for 2019 is as follows (in millions):

	Alliant Energy		IPL		WPL
Defined benefit pension plans (a)		$33.8		$16.5		$15.6
OPEB plans	9.6		1.9		7.4

(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	2019		2020		2021		2022		2023		2024 - 2028
Defined benefit pension benefits		$71.7		$86.1		$74.7		$76.3		$77.8		$388.3
OPEB	19.3		18.1		17.8		17.5		17.0		77.7
		$91.0		$104.2		$92.5		$93.8		$94.8		$466.0

IPL	2019		2020		2021		2022		2023		2024 - 2028
Defined benefit pension benefits		$33.0		$35.1		$35.1		$36.4		$37.5		$182.9
OPEB	7.3		7.3		7.2		7.1		6.9		31.3
		$40.3		$42.4		$42.3		$43.5		$44.4		$214.2

WPL	2019		2020		2021		2022		2023		2024 - 2028
Defined benefit pension benefits		$31.4		$31.8		$31.9		$32.0		$32.5		$165.3
OPEB	8.8		7.6		7.4		7.1		6.8		30.7
		$40.2		$39.4		$39.3		$39.1		$39.3		$196.0

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
	2018		2017		2016		2018		2017		2016		2018		2017		2016
Compensation expense		$17.0		$15.1		$18.0		$9.4		$8.3		$9.5		$6.9		$6.4		$7.9
Income tax benefits	4.9		6.2		7.4		2.8		3.4		4.0		1.9		2.6		3.2

Schedule of Carrying Value and Fair Market Value of the Deferred Compensation Obligation

At December 31, the carrying value of the deferred compensation obligation for the company stock account 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):

	2018		2017
Carrying value		$9.8		$11.1
Fair market value	16.2		19.7

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	2018				2017				2016				2018	2017	2016
Discount rate for benefit obligations	4.34%				3.66%				4.19%				4.24%	3.53%	3.98%
Discount rate for net periodic cost	3.66%				4.19%				4.47%				3.53%	3.98%	4.30%
Expected rate of return on plan assets	7.60%				7.60%				7.60%				5.44%	5.80%	6.30%
Interest crediting rate for Alliant Energy Cash Balance Pension Plan	5.04%				4.64%				3.17%				N/A	N/A	N/A
Rate of compensation increase	3.65	%	-	4.50%	3.65	%	-	4.50%	3.65	%	-	4.50%	N/A	N/A	N/A
Medical cost trend on covered charges:
Initial trend rate (end of year)	N/A				N/A				N/A				6.50%	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	2018	2017	2016	2018	2017	2016
Discount rate for benefit obligations	4.35%	3.68%	4.22%	4.23%	3.51%	3.95%
Discount rate for net periodic cost	3.68%	4.22%	4.50%	3.51%	3.95%	4.28%
Expected rate of return on plan assets	7.60%	7.60%	7.60%	5.60%	6.20%	6.60%
Rate of compensation increase	3.65%	3.65%	3.65%	N/A	N/A	N/A
Medical cost trend on covered charges:
Initial trend rate (end of year)	N/A	N/A	N/A	6.50%	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	2018	2017	2016	2018	2017	2016
Discount rate for benefit obligations	4.35%	3.69%	4.23%	4.23%	3.51%	3.96%
Discount rate for net periodic cost	3.69%	4.23%	4.51%	3.51%	3.96%	4.28%
Expected rate of return on plan assets	7.60%	7.60%	7.60%	3.84%	3.50%	4.70%
Rate of compensation increase	3.65%	3.65%	3.65%	N/A	N/A	N/A
Medical cost trend on covered charges:
Initial trend rate (end of year)	N/A	N/A	N/A	6.50%	6.75%	7.00%
Ultimate trend rate	N/A	N/A	N/A	5.00%	5.00%	5.00%

Net Periodic Benefit Costs

The components of net periodic benefit costs for sponsored defined benefit pension and OPEB plans are included in the tables below (in millions). The service cost component of net periodic benefit costs is included in “Other operation and maintenance” expenses in the income statements and all other components of net periodic benefit costs are included in “Other (income) and deductions” in the income statements.

Alliant Energy	Defined Benefit Pension Plans									OPEB Plans
	2018			2017			2016			2018			2017			2016
Service cost		$12.1			$12.5			$12.6			$4.2			$5.0			$5.3
Interest cost	46.8			51.0			53.0			7.7			8.6			9.4
Expected return on plan assets (a)	(69.7		)	(65.5		)	(65.5		)	(6.0		)	(6.1		)	(6.1		)
Amortization of prior service credit (b)	(0.7		)	(0.4		)	(0.3		)	(0.2		)	(0.2		)	(4.1		)
Amortization of actuarial loss (c)	35.2			37.6			37.4			3.4			3.8			4.7
Settlement losses (d)	—			0.9			—			—			—			—
		$23.7			$36.1			$37.2			$9.1			$11.1			$9.2

IPL	Defined Benefit Pension Plans									OPEB Plans
	2018			2017			2016			2018			2017			2016
Service cost		$7.4			$7.3			$7.5			$1.7			$2.1			$2.3
Interest cost	21.4			23.5			24.5			3.1			3.5			3.8
Expected return on plan assets (a)	(32.6		)	(30.8		)	(30.9		)	(4.4		)	(4.3		)	(4.3		)
Amortization of prior service credit (b)	(0.2		)	(0.2		)	(0.2		)	—			—			(2.6		)
Amortization of actuarial loss (c)	14.9			16.1			16.5			1.3			2.0			2.6
		$10.9			$15.9			$17.4			$1.7			$3.3			$1.8

WPL	Defined Benefit Pension Plans									OPEB Plans
	2018			2017			2016			2018			2017			2016
Service cost		$4.4			$4.9			$4.9			$1.6			$1.9			$2.0
Interest cost	20.2			21.8			22.3			3.1			3.4			3.8
Expected return on plan assets (a)	(30.4		)	(28.5		)	(28.3		)	(0.6		)	(0.8		)	(0.8		)
Amortization of prior service cost (credit) (b)	(0.1		)	0.1			0.2			(0.2		)	(0.2		)	(0.9		)
Amortization of actuarial loss (c)	17.2			18.5			17.6			2.0			1.6			1.8
		$11.3			$16.8			$16.7			$5.9			$5.9			$5.9

(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 Alliant Energy Cash Balance Pension Plan where gains or losses outside the 10% threshold are amortized over the time period the participants are expected to receive benefits.

(d) Settlement losses related to payments made to retired executives of Alliant Energy.

Funded Status Of Benefit Plans

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

	Defined Benefit Pension Plans						OPEB Plans
Alliant Energy	2018			2017			2018			2017
Change in benefit obligation:
Net benefit obligation at January 1		$1,303.1			$1,244.3			$222.3			$220.1
Service cost	12.1			12.5			4.2			5.0
Interest cost	46.8			51.0			7.7			8.6
Plan participants’ contributions	—			—			3.1			2.9
Actuarial (gain) loss	(96.2		)	83.6			(8.2		)	5.4
Gross benefits paid	(90.8		)	(88.3		)	(23.0		)	(19.7		)
Net benefit obligation at December 31	1,175.0			1,303.1			206.1			222.3
Change in plan assets:
Fair value of plan assets at January 1	950.7			895.7			111.1			105.8
Actual return on plan assets	(57.8		)	136.7			(2.6		)	12.9
Employer contributions	6.5			6.6			10.5			9.2
Plan participants’ contributions	—			—			3.1			2.9
Gross benefits paid	(90.8		)	(88.3		)	(23.0		)	(19.7		)
Fair value of plan assets at December 31	808.6			950.7			99.1			111.1
Under funded status at December 31		($366.4	)		($352.4	)		($107.0	)		($111.2	)

	Defined Benefit Pension Plans						OPEB Plans
Alliant Energy	2018			2017			2018			2017
Amounts recognized on the balance sheets consist of:
Non-current assets		$—			$—			$7.5			$8.8
Current liabilities	(2.3		)	(2.2		)	(9.6		)	(9.1		)
Pension and other benefit obligations	(364.1		)	(350.2		)	(104.9		)	(110.9		)
Net amounts recognized at December 31		($366.4	)		($352.4	)		($107.0	)		($111.2	)
Amounts recognized in Regulatory Assets consist of:
Net actuarial loss		$505.2			$509.1			$44.5			$47.4
Prior service credit	(5.8		)	(6.5		)	(1.1		)	(1.3		)
		$499.4			$502.6			$43.4			$46.1

	Defined Benefit Pension Plans						OPEB Plans
IPL	2018			2017			2018			2017
Change in benefit obligation:
Net benefit obligation at January 1		$592.9			$570.4			$89.4			$90.1
Service cost	7.4			7.3			1.7			2.1
Interest cost	21.4			23.5			3.1			3.5
Plan participants’ contributions	—			—			1.0			1.0
Actuarial (gain) loss	(44.4		)	34.9			(4.3		)	(0.1		)
Gross benefits paid	(43.4		)	(43.2		)	(8.4		)	(7.2		)
Net benefit obligation at December 31	533.9			592.9			82.5			89.4
Change in plan assets:
Fair value of plan assets at January 1	443.7			422.0			72.9			68.2
Actual return on plan assets	(26.8		)	64.3			(1.4		)	8.9
Employer contributions	4.3			0.6			2.6			2.0
Plan participants’ contributions	—			—			1.0			1.0
Gross benefits paid	(43.4		)	(43.2		)	(8.4		)	(7.2		)
Fair value of plan assets at December 31	377.8			443.7			66.7			72.9
Under funded status at December 31		($156.1	)		($149.2	)		($15.8	)		($16.5	)

	Defined Benefit Pension Plans						OPEB Plans
IPL	2018			2017			2018			2017
Amounts recognized on the balance sheets consist of:
Non-current assets		$—			$—			$4.7			$5.9
Current liabilities	(0.6		)	(0.5		)	(1.9		)	(2.0		)
Pension and other benefit obligations	(155.5		)	(148.7		)	(18.6		)	(20.4		)
Net amounts recognized at December 31		($156.1	)		($149.2	)		($15.8	)		($16.5	)
Amounts recognized in Regulatory Assets consist of:
Net actuarial loss		$218.8			$218.9			$18.8			$18.7
Prior service credit	(1.8		)	(2.1		)	—			—
		$217.0			$216.8			$18.8			$18.7

	Defined Benefit Pension Plans						OPEB Plans
WPL	2018			2017			2018			2017
Change in benefit obligation:
Net benefit obligation at January 1		$559.8			$529.2			$90.4			$88.9
Service cost	4.4			4.9			1.6			1.9
Interest cost	20.2			21.8			3.1			3.4
Plan participants’ contributions	—			—			1.4			1.4
Actuarial (gain) loss	(40.0		)	38.3			(2.5		)	4.1
Gross benefits paid	(37.8		)	(34.4		)	(10.8		)	(9.3		)
Net benefit obligation at December 31	506.6			559.8			83.2			90.4
Change in plan assets:
Fair value of plan assets at January 1	415.0			389.7			18.7			18.6
Actual return on plan assets	(25.1		)	59.6			(0.1		)	1.2
Employer contributions	0.1			0.1			7.5			6.8
Plan participants’ contributions	—			—			1.4			1.4
Gross benefits paid	(37.8		)	(34.4		)	(10.8		)	(9.3		)
Fair value of plan assets at December 31	352.2			415.0			16.7			18.7
Under funded status at December 31		($154.4	)		($144.8	)		($66.5	)		($71.7	)

	Defined Benefit Pension Plans						OPEB Plans
WPL	2018			2017			2018			2017
Amounts recognized on the balance sheets consist of:
Non-current assets		$—			$—			$2.8			$2.9
Current liabilities	(0.1		)	(0.1		)	(7.4		)	(6.8		)
Pension and other benefit obligations	(154.3		)	(144.7		)	(61.9		)	(67.8		)
Net amounts recognized at December 31		($154.4	)		($144.8	)		($66.5	)		($71.7	)
Amounts recognized in Regulatory Assets consist of:
Net actuarial loss		$223.0			$224.7			$19.9			$23.6
Prior service credit	(1.3		)	(1.5		)	(1.1		)	(1.3		)
		$221.7			$223.2			$18.8			$22.3

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	2018		2017		2018		2017
Accumulated benefit obligations		$1,139.9		$1,269.0		$206.1		$222.3
Plans with accumulated benefit obligations in excess of plan assets:
Accumulated benefit obligations	1,139.9		1,269.0		206.1		222.3
Fair value of plan assets	808.6		950.7		99.1		111.1
Plans with projected benefit obligations in excess of plan assets:
Projected benefit obligations	1,175.0		1,303.1		N/A		N/A
Fair value of plan assets	808.6		950.7		N/A		N/A

	Defined Benefit Pension Plans				OPEB Plans
IPL	2018		2017		2018		2017
Accumulated benefit obligations		$514.3		$573.1		$82.5		$89.4
Plans with accumulated benefit obligations in excess of plan assets:
Accumulated benefit obligations	514.3		573.1		82.5		89.4
Fair value of plan assets	377.8		443.7		66.7		72.9
Plans with projected benefit obligations in excess of plan assets:
Projected benefit obligations	533.9		592.9		N/A		N/A
Fair value of plan assets	377.8		443.7		N/A		N/A

	Defined Benefit Pension Plans				OPEB Plans
WPL	2018		2017		2018		2017
Accumulated benefit obligations		$494.8		$548.1		$83.2		$90.4
Plans with accumulated benefit obligations in excess of plan assets:
Accumulated benefit obligations	494.8		548.1		83.2		90.4
Fair value of plan assets	352.2		415.0		16.7		18.7
Plans with projected benefit obligations in excess of plan assets:
Projected benefit obligations	506.6		559.8		N/A		N/A
Fair value of plan assets	352.2		415.0		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
	2018		2017		2018		2017
Regulatory assets		$38.2		$38.9		$27.7		$28.1

Estimated Future Employer Contributions

Estimated funding for the qualified and non-qualified defined benefit pension and OPEB plans for 2019 is as follows (in millions):

	Alliant Energy		IPL		WPL
Defined benefit pension plans (a)		$33.8		$16.5		$15.6
OPEB plans	9.6		1.9		7.4

(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	2019		2020		2021		2022		2023		2024 - 2028
Defined benefit pension benefits		$71.7		$86.1		$74.7		$76.3		$77.8		$388.3
OPEB	19.3		18.1		17.8		17.5		17.0		77.7
		$91.0		$104.2		$92.5		$93.8		$94.8		$466.0

IPL	2019		2020		2021		2022		2023		2024 - 2028
Defined benefit pension benefits		$33.0		$35.1		$35.1		$36.4		$37.5		$182.9
OPEB	7.3		7.3		7.2		7.1		6.9		31.3
		$40.3		$42.4		$42.3		$43.5		$44.4		$214.2

WPL	2019		2020		2021		2022		2023		2024 - 2028
Defined benefit pension benefits		$31.4		$31.8		$31.9		$32.0		$32.5		$165.3
OPEB	8.8		7.6		7.4		7.1		6.8		30.7
		$40.2		$39.4		$39.3		$39.1		$39.3		$196.0

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
	2018		2017		2016		2018		2017		2016		2018		2017		2016
Compensation expense		$17.0		$15.1		$18.0		$9.4		$8.3		$9.5		$6.9		$6.4		$7.9
Income tax benefits	4.9		6.2		7.4		2.8		3.4		4.0		1.9		2.6		3.2

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	2018				2017				2016				2018	2017	2016
Discount rate for benefit obligations	4.34%				3.66%				4.19%				4.24%	3.53%	3.98%
Discount rate for net periodic cost	3.66%				4.19%				4.47%				3.53%	3.98%	4.30%
Expected rate of return on plan assets	7.60%				7.60%				7.60%				5.44%	5.80%	6.30%
Interest crediting rate for Alliant Energy Cash Balance Pension Plan	5.04%				4.64%				3.17%				N/A	N/A	N/A
Rate of compensation increase	3.65	%	-	4.50%	3.65	%	-	4.50%	3.65	%	-	4.50%	N/A	N/A	N/A
Medical cost trend on covered charges:
Initial trend rate (end of year)	N/A				N/A				N/A				6.50%	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	2018	2017	2016	2018	2017	2016
Discount rate for benefit obligations	4.35%	3.68%	4.22%	4.23%	3.51%	3.95%
Discount rate for net periodic cost	3.68%	4.22%	4.50%	3.51%	3.95%	4.28%
Expected rate of return on plan assets	7.60%	7.60%	7.60%	5.60%	6.20%	6.60%
Rate of compensation increase	3.65%	3.65%	3.65%	N/A	N/A	N/A
Medical cost trend on covered charges:
Initial trend rate (end of year)	N/A	N/A	N/A	6.50%	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	2018	2017	2016	2018	2017	2016
Discount rate for benefit obligations	4.35%	3.69%	4.23%	4.23%	3.51%	3.96%
Discount rate for net periodic cost	3.69%	4.23%	4.51%	3.51%	3.96%	4.28%
Expected rate of return on plan assets	7.60%	7.60%	7.60%	3.84%	3.50%	4.70%
Rate of compensation increase	3.65%	3.65%	3.65%	N/A	N/A	N/A
Medical cost trend on covered charges:
Initial trend rate (end of year)	N/A	N/A	N/A	6.50%	6.75%	7.00%
Ultimate trend rate	N/A	N/A	N/A	5.00%	5.00%	5.00%

Net Periodic Benefit Costs

The components of net periodic benefit costs for sponsored defined benefit pension and OPEB plans are included in the tables below (in millions). The service cost component of net periodic benefit costs is included in “Other operation and maintenance” expenses in the income statements and all other components of net periodic benefit costs are included in “Other (income) and deductions” in the income statements.

Alliant Energy	Defined Benefit Pension Plans									OPEB Plans
	2018			2017			2016			2018			2017			2016
Service cost		$12.1			$12.5			$12.6			$4.2			$5.0			$5.3
Interest cost	46.8			51.0			53.0			7.7			8.6			9.4
Expected return on plan assets (a)	(69.7		)	(65.5		)	(65.5		)	(6.0		)	(6.1		)	(6.1		)
Amortization of prior service credit (b)	(0.7		)	(0.4		)	(0.3		)	(0.2		)	(0.2		)	(4.1		)
Amortization of actuarial loss (c)	35.2			37.6			37.4			3.4			3.8			4.7
Settlement losses (d)	—			0.9			—			—			—			—
		$23.7			$36.1			$37.2			$9.1			$11.1			$9.2

IPL	Defined Benefit Pension Plans									OPEB Plans
	2018			2017			2016			2018			2017			2016
Service cost		$7.4			$7.3			$7.5			$1.7			$2.1			$2.3
Interest cost	21.4			23.5			24.5			3.1			3.5			3.8
Expected return on plan assets (a)	(32.6		)	(30.8		)	(30.9		)	(4.4		)	(4.3		)	(4.3		)
Amortization of prior service credit (b)	(0.2		)	(0.2		)	(0.2		)	—			—			(2.6		)
Amortization of actuarial loss (c)	14.9			16.1			16.5			1.3			2.0			2.6
		$10.9			$15.9			$17.4			$1.7			$3.3			$1.8

WPL	Defined Benefit Pension Plans									OPEB Plans
	2018			2017			2016			2018			2017			2016
Service cost		$4.4			$4.9			$4.9			$1.6			$1.9			$2.0
Interest cost	20.2			21.8			22.3			3.1			3.4			3.8
Expected return on plan assets (a)	(30.4		)	(28.5		)	(28.3		)	(0.6		)	(0.8		)	(0.8		)
Amortization of prior service cost (credit) (b)	(0.1		)	0.1			0.2			(0.2		)	(0.2		)	(0.9		)
Amortization of actuarial loss (c)	17.2			18.5			17.6			2.0			1.6			1.8
		$11.3			$16.8			$16.7			$5.9			$5.9			$5.9

(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 Alliant Energy Cash Balance Pension Plan where gains or losses outside the 10% threshold are amortized over the time period the participants are expected to receive benefits.

(d) Settlement losses related to payments made to retired executives of Alliant Energy.

Funded Status Of Benefit Plans

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

	Defined Benefit Pension Plans						OPEB Plans
Alliant Energy	2018			2017			2018			2017
Change in benefit obligation:
Net benefit obligation at January 1		$1,303.1			$1,244.3			$222.3			$220.1
Service cost	12.1			12.5			4.2			5.0
Interest cost	46.8			51.0			7.7			8.6
Plan participants’ contributions	—			—			3.1			2.9
Actuarial (gain) loss	(96.2		)	83.6			(8.2		)	5.4
Gross benefits paid	(90.8		)	(88.3		)	(23.0		)	(19.7		)
Net benefit obligation at December 31	1,175.0			1,303.1			206.1			222.3
Change in plan assets:
Fair value of plan assets at January 1	950.7			895.7			111.1			105.8
Actual return on plan assets	(57.8		)	136.7			(2.6		)	12.9
Employer contributions	6.5			6.6			10.5			9.2
Plan participants’ contributions	—			—			3.1			2.9
Gross benefits paid	(90.8		)	(88.3		)	(23.0		)	(19.7		)
Fair value of plan assets at December 31	808.6			950.7			99.1			111.1
Under funded status at December 31		($366.4	)		($352.4	)		($107.0	)		($111.2	)

	Defined Benefit Pension Plans						OPEB Plans
Alliant Energy	2018			2017			2018			2017
Amounts recognized on the balance sheets consist of:
Non-current assets		$—			$—			$7.5			$8.8
Current liabilities	(2.3		)	(2.2		)	(9.6		)	(9.1		)
Pension and other benefit obligations	(364.1		)	(350.2		)	(104.9		)	(110.9		)
Net amounts recognized at December 31		($366.4	)		($352.4	)		($107.0	)		($111.2	)
Amounts recognized in Regulatory Assets consist of:
Net actuarial loss		$505.2			$509.1			$44.5			$47.4
Prior service credit	(5.8		)	(6.5		)	(1.1		)	(1.3		)
		$499.4			$502.6			$43.4			$46.1

	Defined Benefit Pension Plans						OPEB Plans
IPL	2018			2017			2018			2017
Change in benefit obligation:
Net benefit obligation at January 1		$592.9			$570.4			$89.4			$90.1
Service cost	7.4			7.3			1.7			2.1
Interest cost	21.4			23.5			3.1			3.5
Plan participants’ contributions	—			—			1.0			1.0
Actuarial (gain) loss	(44.4		)	34.9			(4.3		)	(0.1		)
Gross benefits paid	(43.4		)	(43.2		)	(8.4		)	(7.2		)
Net benefit obligation at December 31	533.9			592.9			82.5			89.4
Change in plan assets:
Fair value of plan assets at January 1	443.7			422.0			72.9			68.2
Actual return on plan assets	(26.8		)	64.3			(1.4		)	8.9
Employer contributions	4.3			0.6			2.6			2.0
Plan participants’ contributions	—			—			1.0			1.0
Gross benefits paid	(43.4		)	(43.2		)	(8.4		)	(7.2		)
Fair value of plan assets at December 31	377.8			443.7			66.7			72.9
Under funded status at December 31		($156.1	)		($149.2	)		($15.8	)		($16.5	)

	Defined Benefit Pension Plans						OPEB Plans
IPL	2018			2017			2018			2017
Amounts recognized on the balance sheets consist of:
Non-current assets		$—			$—			$4.7			$5.9
Current liabilities	(0.6		)	(0.5		)	(1.9		)	(2.0		)
Pension and other benefit obligations	(155.5		)	(148.7		)	(18.6		)	(20.4		)
Net amounts recognized at December 31		($156.1	)		($149.2	)		($15.8	)		($16.5	)
Amounts recognized in Regulatory Assets consist of:
Net actuarial loss		$218.8			$218.9			$18.8			$18.7
Prior service credit	(1.8		)	(2.1		)	—			—
		$217.0			$216.8			$18.8			$18.7

	Defined Benefit Pension Plans						OPEB Plans
WPL	2018			2017			2018			2017
Change in benefit obligation:
Net benefit obligation at January 1		$559.8			$529.2			$90.4			$88.9
Service cost	4.4			4.9			1.6			1.9
Interest cost	20.2			21.8			3.1			3.4
Plan participants’ contributions	—			—			1.4			1.4
Actuarial (gain) loss	(40.0		)	38.3			(2.5		)	4.1
Gross benefits paid	(37.8		)	(34.4		)	(10.8		)	(9.3		)
Net benefit obligation at December 31	506.6			559.8			83.2			90.4
Change in plan assets:
Fair value of plan assets at January 1	415.0			389.7			18.7			18.6
Actual return on plan assets	(25.1		)	59.6			(0.1		)	1.2
Employer contributions	0.1			0.1			7.5			6.8
Plan participants’ contributions	—			—			1.4			1.4
Gross benefits paid	(37.8		)	(34.4		)	(10.8		)	(9.3		)
Fair value of plan assets at December 31	352.2			415.0			16.7			18.7
Under funded status at December 31		($154.4	)		($144.8	)		($66.5	)		($71.7	)

	Defined Benefit Pension Plans						OPEB Plans
WPL	2018			2017			2018			2017
Amounts recognized on the balance sheets consist of:
Non-current assets		$—			$—			$2.8			$2.9
Current liabilities	(0.1		)	(0.1		)	(7.4		)	(6.8		)
Pension and other benefit obligations	(154.3		)	(144.7		)	(61.9		)	(67.8		)
Net amounts recognized at December 31		($154.4	)		($144.8	)		($66.5	)		($71.7	)
Amounts recognized in Regulatory Assets consist of:
Net actuarial loss		$223.0			$224.7			$19.9			$23.6
Prior service credit	(1.3		)	(1.5		)	(1.1		)	(1.3		)
		$221.7			$223.2			$18.8			$22.3

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	2018		2017		2018		2017
Accumulated benefit obligations		$1,139.9		$1,269.0		$206.1		$222.3
Plans with accumulated benefit obligations in excess of plan assets:
Accumulated benefit obligations	1,139.9		1,269.0		206.1		222.3
Fair value of plan assets	808.6		950.7		99.1		111.1
Plans with projected benefit obligations in excess of plan assets:
Projected benefit obligations	1,175.0		1,303.1		N/A		N/A
Fair value of plan assets	808.6		950.7		N/A		N/A

	Defined Benefit Pension Plans				OPEB Plans
IPL	2018		2017		2018		2017
Accumulated benefit obligations		$514.3		$573.1		$82.5		$89.4
Plans with accumulated benefit obligations in excess of plan assets:
Accumulated benefit obligations	514.3		573.1		82.5		89.4
Fair value of plan assets	377.8		443.7		66.7		72.9
Plans with projected benefit obligations in excess of plan assets:
Projected benefit obligations	533.9		592.9		N/A		N/A
Fair value of plan assets	377.8		443.7		N/A		N/A

	Defined Benefit Pension Plans				OPEB Plans
WPL	2018		2017		2018		2017
Accumulated benefit obligations		$494.8		$548.1		$83.2		$90.4
Plans with accumulated benefit obligations in excess of plan assets:
Accumulated benefit obligations	494.8		548.1		83.2		90.4
Fair value of plan assets	352.2		415.0		16.7		18.7
Plans with projected benefit obligations in excess of plan assets:
Projected benefit obligations	506.6		559.8		N/A		N/A
Fair value of plan assets	352.2		415.0		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
	2018		2017		2018		2017
Regulatory assets		$38.2		$38.9		$27.7		$28.1

Estimated Future Employer Contributions

Estimated funding for the qualified and non-qualified defined benefit pension and OPEB plans for 2019 is as follows (in millions):

	Alliant Energy		IPL		WPL
Defined benefit pension plans (a)		$33.8		$16.5		$15.6
OPEB plans	9.6		1.9		7.4

(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	2019		2020		2021		2022		2023		2024 - 2028
Defined benefit pension benefits		$71.7		$86.1		$74.7		$76.3		$77.8		$388.3
OPEB	19.3		18.1		17.8		17.5		17.0		77.7
		$91.0		$104.2		$92.5		$93.8		$94.8		$466.0

IPL	2019		2020		2021		2022		2023		2024 - 2028
Defined benefit pension benefits		$33.0		$35.1		$35.1		$36.4		$37.5		$182.9
OPEB	7.3		7.3		7.2		7.1		6.9		31.3
		$40.3		$42.4		$42.3		$43.5		$44.4		$214.2

WPL	2019		2020		2021		2022		2023		2024 - 2028
Defined benefit pension benefits		$31.4		$31.8		$31.9		$32.0		$32.5		$165.3
OPEB	8.8		7.6		7.4		7.1		6.8		30.7
		$40.2		$39.4		$39.3		$39.1		$39.3		$196.0

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
	2018		2017		2016		2018		2017		2016		2018		2017		2016
Compensation expense		$17.0		$15.1		$18.0		$9.4		$8.3		$9.5		$6.9		$6.4		$7.9
Income tax benefits	4.9		6.2		7.4		2.8		3.4		4.0		1.9		2.6		3.2

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, 2018, 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%	4%
Equity securities - U.S.	11	%	-	41%	25%
Equity securities - international	14	%	-	34%	22%
Global asset securities	5	%	-	15%	9%
Risk parity securities	5	%	-	15%	10%
Fixed income securities	20	%	-	40%	30%

At December 31, the fair values of qualified and non-qualified defined benefit pension plan assets were as follows (in millions):

	2018									2017
	Fair			Level		Level		Level		Fair			Level		Level		Level
Alliant Energy	Value			1		2		3		Value			1		2		3
Cash and equivalents		$36.4			$3.0		$33.4		$—		$28.2			$4.5		$23.7		$—
Equity securities - U.S.	130.2			130.2		—		—		158.3			158.3		—		—
Equity securities - international	116.0			116.0		—		—		137.5			137.5		—		—
Global asset securities	42.1			42.1		—		—		49.4			49.4		—		—
Fixed income securities	127.8			52.5		75.3		—		135.9			55.8		80.1		—
Total assets in fair value hierarchy	452.5				$343.8		$108.7		$—	509.3				$405.5		$103.8		$—
Assets measured at net asset value	355.4									441.1
Accrued investment income	1.2									1.0
Due to brokers, net (pending trades with brokers)	(0.5		)							(0.7		)
Total pension plan assets		$808.6									$950.7

	2018									2017
	Fair			Level		Level		Level		Fair			Level		Level		Level
IPL	Value			1		2		3		Value			1		2		3
Cash and equivalents		$17.0			$1.4		$15.6		$—		$13.2			$2.2		$11.0		$—
Equity securities - U.S.	60.8			60.8		—		—		73.9			73.9		—		—
Equity securities - international	54.2			54.2		—		—		64.2			64.2		—		—
Global asset securities	19.7			19.7		—		—		23.0			23.0		—		—
Fixed income securities	59.7			24.5		35.2		—		63.4			26.0		37.4		—
Total assets in fair value hierarchy	211.4				$160.6		$50.8		$—	237.7				$189.3		$48.4		$—
Assets measured at net asset value	166.1									205.8
Accrued investment income	0.6									0.5
Due to brokers, net (pending trades with brokers)	(0.3		)							(0.3		)
Total pension plan assets		$377.8									$443.7

	2018									2017
	Fair			Level		Level		Level		Fair			Level		Level		Level
WPL	Value			1		2		3		Value			1		2		3
Cash and equivalents		$15.9			$1.3		$14.6		$—		$12.3			$2.0		$10.3		$—
Equity securities - U.S.	56.7			56.7		—		—		69.1			69.1		—		—
Equity securities - international	50.5			50.5		—		—		60.0			60.0		—		—
Global asset securities	18.4			18.4		—		—		21.6			21.6		—		—
Fixed income securities	55.6			22.8		32.8		—		59.3			24.3		35.0		—
Total assets in fair value hierarchy	197.1				$149.7		$47.4		$—	222.3				$177.0		$45.3		$—
Assets measured at net asset value	154.8									192.5
Accrued investment income	0.5									0.5
Due to brokers, net (pending trades with brokers)	(0.2		)							(0.3		)
Total pension plan assets		$352.2									$415.0

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, the fair values of qualified and non-qualified defined benefit pension plan assets were as follows (in millions):

	2018									2017
	Fair			Level		Level		Level		Fair			Level		Level		Level
Alliant Energy	Value			1		2		3		Value			1		2		3
Cash and equivalents		$36.4			$3.0		$33.4		$—		$28.2			$4.5		$23.7		$—
Equity securities - U.S.	130.2			130.2		—		—		158.3			158.3		—		—
Equity securities - international	116.0			116.0		—		—		137.5			137.5		—		—
Global asset securities	42.1			42.1		—		—		49.4			49.4		—		—
Fixed income securities	127.8			52.5		75.3		—		135.9			55.8		80.1		—
Total assets in fair value hierarchy	452.5				$343.8		$108.7		$—	509.3				$405.5		$103.8		$—
Assets measured at net asset value	355.4									441.1
Accrued investment income	1.2									1.0
Due to brokers, net (pending trades with brokers)	(0.5		)							(0.7		)
Total pension plan assets		$808.6									$950.7

	2018									2017
	Fair			Level		Level		Level		Fair			Level		Level		Level
IPL	Value			1		2		3		Value			1		2		3
Cash and equivalents		$17.0			$1.4		$15.6		$—		$13.2			$2.2		$11.0		$—
Equity securities - U.S.	60.8			60.8		—		—		73.9			73.9		—		—
Equity securities - international	54.2			54.2		—		—		64.2			64.2		—		—
Global asset securities	19.7			19.7		—		—		23.0			23.0		—		—
Fixed income securities	59.7			24.5		35.2		—		63.4			26.0		37.4		—
Total assets in fair value hierarchy	211.4				$160.6		$50.8		$—	237.7				$189.3		$48.4		$—
Assets measured at net asset value	166.1									205.8
Accrued investment income	0.6									0.5
Due to brokers, net (pending trades with brokers)	(0.3		)							(0.3		)
Total pension plan assets		$377.8									$443.7

	2018									2017
	Fair			Level		Level		Level		Fair			Level		Level		Level
WPL	Value			1		2		3		Value			1		2		3
Cash and equivalents		$15.9			$1.3		$14.6		$—		$12.3			$2.0		$10.3		$—
Equity securities - U.S.	56.7			56.7		—		—		69.1			69.1		—		—
Equity securities - international	50.5			50.5		—		—		60.0			60.0		—		—
Global asset securities	18.4			18.4		—		—		21.6			21.6		—		—
Fixed income securities	55.6			22.8		32.8		—		59.3			24.3		35.0		—
Total assets in fair value hierarchy	197.1				$149.7		$47.4		$—	222.3				$177.0		$45.3		$—
Assets measured at net asset value	154.8									192.5
Accrued investment income	0.5									0.5
Due to brokers, net (pending trades with brokers)	(0.2		)							(0.3		)
Total pension plan assets		$352.2									$415.0

At December 31, 2018, 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%	4%
Equity securities - U.S.	11	%	-	41%	25%
Equity securities - international	14	%	-	34%	22%
Global asset securities	5	%	-	15%	9%
Risk parity securities	5	%	-	15%	10%
Fixed income securities	20	%	-	40%	30%

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 qualified and non-qualified defined benefit pension plan assets were as follows (in millions):

	2018									2017
	Fair			Level		Level		Level		Fair			Level		Level		Level
Alliant Energy	Value			1		2		3		Value			1		2		3
Cash and equivalents		$36.4			$3.0		$33.4		$—		$28.2			$4.5		$23.7		$—
Equity securities - U.S.	130.2			130.2		—		—		158.3			158.3		—		—
Equity securities - international	116.0			116.0		—		—		137.5			137.5		—		—
Global asset securities	42.1			42.1		—		—		49.4			49.4		—		—
Fixed income securities	127.8			52.5		75.3		—		135.9			55.8		80.1		—
Total assets in fair value hierarchy	452.5				$343.8		$108.7		$—	509.3				$405.5		$103.8		$—
Assets measured at net asset value	355.4									441.1
Accrued investment income	1.2									1.0
Due to brokers, net (pending trades with brokers)	(0.5		)							(0.7		)
Total pension plan assets		$808.6									$950.7

	2018									2017
	Fair			Level		Level		Level		Fair			Level		Level		Level
IPL	Value			1		2		3		Value			1		2		3
Cash and equivalents		$17.0			$1.4		$15.6		$—		$13.2			$2.2		$11.0		$—
Equity securities - U.S.	60.8			60.8		—		—		73.9			73.9		—		—
Equity securities - international	54.2			54.2		—		—		64.2			64.2		—		—
Global asset securities	19.7			19.7		—		—		23.0			23.0		—		—
Fixed income securities	59.7			24.5		35.2		—		63.4			26.0		37.4		—
Total assets in fair value hierarchy	211.4				$160.6		$50.8		$—	237.7				$189.3		$48.4		$—
Assets measured at net asset value	166.1									205.8
Accrued investment income	0.6									0.5
Due to brokers, net (pending trades with brokers)	(0.3		)							(0.3		)
Total pension plan assets		$377.8									$443.7

	2018									2017
	Fair			Level		Level		Level		Fair			Level		Level		Level
WPL	Value			1		2		3		Value			1		2		3
Cash and equivalents		$15.9			$1.3		$14.6		$—		$12.3			$2.0		$10.3		$—
Equity securities - U.S.	56.7			56.7		—		—		69.1			69.1		—		—
Equity securities - international	50.5			50.5		—		—		60.0			60.0		—		—
Global asset securities	18.4			18.4		—		—		21.6			21.6		—		—
Fixed income securities	55.6			22.8		32.8		—		59.3			24.3		35.0		—
Total assets in fair value hierarchy	197.1				$149.7		$47.4		$—	222.3				$177.0		$45.3		$—
Assets measured at net asset value	154.8									192.5
Accrued investment income	0.5									0.5
Due to brokers, net (pending trades with brokers)	(0.2		)							(0.3		)
Total pension plan assets		$352.2									$415.0

At December 31, 2018, 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%	4%
Equity securities - U.S.	11	%	-	41%	25%
Equity securities - international	14	%	-	34%	22%
Global asset securities	5	%	-	15%	9%
Risk parity securities	5	%	-	15%	10%
Fixed income securities	20	%	-	40%	30%

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, 2018, 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	%	-	5%	1%
Equity securities - U.S.	0	%	-	46%	24%
Equity securities - international	0	%	-	34%	2%
Fixed income securities	20	%	-	100%	73%

At December 31, the fair values of OPEB plan assets were as follows (in millions):

	2018								2017
	Fair		Level		Level		Level		Fair		Level		Level		Level
Alliant Energy	Value		1		2		3		Value		1		2		3
Cash and equivalents		$1.4		$1.1		$0.3		$—		$1.2		$0.7		$0.5		$—
Equity securities - U.S.	3.9		3.9		—		—		27.9		27.9		—		—
Equity securities - international	2.9		2.9		—		—		11.4		11.4		—		—
Global asset securities	0.4		0.4		—		—		0.4		0.4		—		—
Fixed income securities	68.2		67.5		0.7		—		66.6		66.0		0.6		—
Total assets in fair value hierarchy	76.8			$75.8		$1.0		$—	107.5			$106.4		$1.1		$—
Assets measured at net asset value	22.3								3.6
Total OPEB plan assets		$99.1								$111.1

	2018								2017
	Fair		Level		Level		Level		Fair		Level		Level		Level
IPL	Value		1		2		3		Value		1		2		3
Cash and equivalents		$0.7		$0.7		$—		$—		$0.3		$0.3		$—		$—
Equity securities - U.S.	—		—		—		—		22.3		22.3		—		—
Equity securities - international	—		—		—		—		7.5		7.5		—		—
Fixed income securities	47.0		47.0		—		—		42.8		42.8		—		—
Total assets in fair value hierarchy	47.7			$47.7		$—		$—	72.9			$72.9		$—		$—
Assets measured at net asset value	19.0								—
Total OPEB plan assets		$66.7								$72.9

	2018								2017
	Fair		Level		Level		Level		Fair		Level		Level		Level
WPL	Value		1		2		3		Value		1		2		3
Cash and equivalents		$0.1		$0.1		$—		$—		$0.6		$0.3		$0.3		$—
Fixed income securities	16.6		16.6		—		—		18.1		18.1		—		—
Total OPEB plan assets		$16.7		$16.7		$—		$—		$18.7		$18.4		$0.3		$—

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, 2018, 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	%	-	5%	1%
Equity securities - U.S.	0	%	-	46%	24%
Equity securities - international	0	%	-	34%	2%
Fixed income securities	20	%	-	100%	73%

At December 31, the fair values of OPEB plan assets were as follows (in millions):

	2018								2017
	Fair		Level		Level		Level		Fair		Level		Level		Level
Alliant Energy	Value		1		2		3		Value		1		2		3
Cash and equivalents		$1.4		$1.1		$0.3		$—		$1.2		$0.7		$0.5		$—
Equity securities - U.S.	3.9		3.9		—		—		27.9		27.9		—		—
Equity securities - international	2.9		2.9		—		—		11.4		11.4		—		—
Global asset securities	0.4		0.4		—		—		0.4		0.4		—		—
Fixed income securities	68.2		67.5		0.7		—		66.6		66.0		0.6		—
Total assets in fair value hierarchy	76.8			$75.8		$1.0		$—	107.5			$106.4		$1.1		$—
Assets measured at net asset value	22.3								3.6
Total OPEB plan assets		$99.1								$111.1

	2018								2017
	Fair		Level		Level		Level		Fair		Level		Level		Level
IPL	Value		1		2		3		Value		1		2		3
Cash and equivalents		$0.7		$0.7		$—		$—		$0.3		$0.3		$—		$—
Equity securities - U.S.	—		—		—		—		22.3		22.3		—		—
Equity securities - international	—		—		—		—		7.5		7.5		—		—
Fixed income securities	47.0		47.0		—		—		42.8		42.8		—		—
Total assets in fair value hierarchy	47.7			$47.7		$—		$—	72.9			$72.9		$—		$—
Assets measured at net asset value	19.0								—
Total OPEB plan assets		$66.7								$72.9

	2018								2017
	Fair		Level		Level		Level		Fair		Level		Level		Level
WPL	Value		1		2		3		Value		1		2		3
Cash and equivalents		$0.1		$0.1		$—		$—		$0.6		$0.3		$0.3		$—
Fixed income securities	16.6		16.6		—		—		18.1		18.1		—		—
Total OPEB plan assets		$16.7		$16.7		$—		$—		$18.7		$18.4		$0.3		$—

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, 2018, 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	%	-	5%	1%
Equity securities - U.S.	0	%	-	46%	24%
Equity securities - international	0	%	-	34%	2%
Fixed income securities	20	%	-	100%	73%

At December 31, the fair values of OPEB plan assets were as follows (in millions):

	2018								2017
	Fair		Level		Level		Level		Fair		Level		Level		Level
Alliant Energy	Value		1		2		3		Value		1		2		3
Cash and equivalents		$1.4		$1.1		$0.3		$—		$1.2		$0.7		$0.5		$—
Equity securities - U.S.	3.9		3.9		—		—		27.9		27.9		—		—
Equity securities - international	2.9		2.9		—		—		11.4		11.4		—		—
Global asset securities	0.4		0.4		—		—		0.4		0.4		—		—
Fixed income securities	68.2		67.5		0.7		—		66.6		66.0		0.6		—
Total assets in fair value hierarchy	76.8			$75.8		$1.0		$—	107.5			$106.4		$1.1		$—
Assets measured at net asset value	22.3								3.6
Total OPEB plan assets		$99.1								$111.1

	2018								2017
	Fair		Level		Level		Level		Fair		Level		Level		Level
IPL	Value		1		2		3		Value		1		2		3
Cash and equivalents		$0.7		$0.7		$—		$—		$0.3		$0.3		$—		$—
Equity securities - U.S.	—		—		—		—		22.3		22.3		—		—
Equity securities - international	—		—		—		—		7.5		7.5		—		—
Fixed income securities	47.0		47.0		—		—		42.8		42.8		—		—
Total assets in fair value hierarchy	47.7			$47.7		$—		$—	72.9			$72.9		$—		$—
Assets measured at net asset value	19.0								—
Total OPEB plan assets		$66.7								$72.9

	2018								2017
	Fair		Level		Level		Level		Fair		Level		Level		Level
WPL	Value		1		2		3		Value		1		2		3
Cash and equivalents		$0.1		$0.1		$—		$—		$0.6		$0.3		$0.3		$—
Fixed income securities	16.6		16.6		—		—		18.1		18.1		—		—
Total OPEB plan assets		$16.7		$16.7		$—		$—		$18.7		$18.4		$0.3		$—

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
	2018		2017		2016		2018		2017		2016		2018		2017		2016
401(k) costs		$25.1		$24.8		$23.6		$13.0		$12.8		$12.0		$11.2		$11.1		$10.7

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
	2018		2017		2016		2018		2017		2016		2018		2017		2016
401(k) costs		$25.1		$24.8		$23.6		$13.0		$12.8		$12.0		$11.2		$11.1		$10.7

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
	2018		2017		2016		2018		2017		2016		2018		2017		2016
401(k) costs		$25.1		$24.8		$23.6		$13.0		$12.8		$12.0		$11.2		$11.1		$10.7

Performance Shares and Performance Units [Member]

Defined Benefit Plan Disclosure [Line Items]

Schedule Of Equity-based Compensation Plans Activity

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

	Performance Shares						Performance Units
	2018		2017		2016		2018		2017		2016
Nonvested awards, January 1	223,511		257,599		288,430		71,737		93,320		116,412
Granted	74,163		65,350		68,585		19,840		21,558		23,918
Vested	(90,806	)	(99,438	)	(98,186	)	(31,910	)	(37,395	)	(42,760	)
Forfeited	(3,680	)	—		(1,230	)	(1,906	)	(5,746	)	(4,250	)
Nonvested awards, December 31	203,188		223,511		257,599		57,761		71,737		93,320

Granted Awards - Each performance share’s and performance unit’s value is based on the closing market price of one share of Alliant Energy’s common stock at the end of the performance period. The actual payout for performance shares and performance units is dependent upon actual performance and may range from zero to 200% of the target number of awards. 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 - 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
	2018	2017	2016	2018	2017	2016
	2015 Grant	2014 Grant	2013 Grant	2015 Grant	2014 Grant	2013 Grant
Performance awards vested	90,806	99,438	98,186	31,910	37,395	42,760
Percentage of target number of performance awards	137.5%	147.5%	165.0%	137.5%	147.5%	165.0%
Aggregate payout value (in millions)	$5.3	$5.6	$5.1	$1.4	$1.5	$1.7
Payout - cash (in millions)	$4.9	$5.1	$2.9	$1.4	$1.5	$1.7
Payout - common stock shares issued	5,078	5,185	22,408	N/A	N/A	N/A

Fair Value of Awards - At December 31, 2018, Alliant Energy’s common stock closing price was $42.25. Additional information related to fair values of nonvested performance shares and performance units at December 31, 2018, by year of grant, was as follows:

	Performance Shares									Performance Units
	2018 Grant			2017 Grant			2016 Grant			2018 Grant			2017 Grant			2016 Grant
Nonvested awards at target	70,483			65,350			67,355			19,196			18,062			20,503
Estimated payout percentage based on performance criteria	85		%	85		%	143		%	85		%	85		%	143		%
Fair values of each nonvested award		$35.91			$35.91			$60.42			$35.91			$35.91			$60.42

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:

	2018				2017			2016
	Units		Weighted Average Grant Date Fair Value		Units	Weighted Average Grant Date Fair Value		Units		Weighted Average Grant Date Fair Value
Nonvested units, January 1	132,705			$36.50	67,355		$33.96	—			$—
Granted	74,163		38.60		65,350	39.12		68,585		33.96
Forfeited	(3,680	)	38.60		—	—		(1,230	)	33.90
Nonvested units, December 31	203,188		37.23		132,705	36.50		67,355		33.96

Restricted Stock Units [Member]

Defined Benefit Plan Disclosure [Line Items]

Schedule Of Equity-based Compensation Plans Activity

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

	2018		2017	2016
Nonvested units, January 1	113,749		57,736	—
Granted	63,568		56,013	58,790
Forfeited	(3,154	)	—	(1,054	)
Nonvested units, December 31	174,163		113,749	57,736