Benefit Plans (Tables)

12 Months Ended

Dec. 31, 2019

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	2019				2018				2017				2019	2018	2017
Discount rate for benefit obligations	3.48%				4.34%				3.66%				3.40%	4.24%	3.53%
Discount rate for net periodic cost	4.34%				3.66%				4.19%				4.24%	3.53%	3.98%
Expected rate of return on plan assets	7.60%				7.60%				7.60%				5.44%	5.44%	5.80%
Interest crediting rate for Alliant Energy Cash Balance Pension Plan	5.52%				5.04%				4.64%				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

	Qualified Defined Benefit Pension Plan			OPEB Plans
IPL	2019	2018	2017	2019	2018	2017
Discount rate for benefit obligations	3.51%	4.35%	3.68%	3.39%	4.23%	3.51%
Discount rate for net periodic cost	4.35%	3.68%	4.22%	4.23%	3.51%	3.95%
Expected rate of return on plan assets	7.60%	7.60%	7.60%	5.60%	5.60%	6.20%
Rate of compensation increase	3.65%	3.65%	3.65%	N/A	N/A	N/A

	Qualified Defined Benefit Pension Plan			OPEB Plans
WPL	2019	2018	2017	2019	2018	2017
Discount rate for benefit obligations	3.50%	4.35%	3.69%	3.39%	4.23%	3.51%
Discount rate for net periodic cost	4.35%	3.69%	4.23%	4.23%	3.51%	3.96%
Expected rate of return on plan assets	7.60%	7.60%	7.60%	3.81%	3.84%	3.50%
Rate of compensation increase	3.65%	3.65%	3.65%	N/A	N/A	N/A

Net Periodic Benefit Costs

The components of net periodic benefit costs for sponsored defined benefit pension and OPEB plans are included 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
	2019			2018			2017			2019			2018			2017
Service cost		$9.7			$12.1			$12.5			$3.3			$4.2			$5.0
Interest cost	49.8			46.8			51.0			8.5			7.7			8.6
Expected return on plan assets (a)	(60.1		)	(69.7		)	(65.5		)	(5.0		)	(6.0		)	(6.1		)
Amortization of prior service credit (b)	(0.7		)	(0.7		)	(0.4		)	(0.2		)	(0.2		)	(0.2		)
Amortization of actuarial loss (c)	36.4			35.2			37.6			3.3			3.4			3.8
Settlement losses (d)	—			—			0.9			—			—			—
		$35.1			$23.7			$36.1			$9.9			$9.1			$11.1

IPL	Defined Benefit Pension Plans									OPEB Plans
	2019			2018			2017			2019			2018			2017
Service cost		$6.0			$7.4			$7.3			$1.3			$1.7			$2.1
Interest cost	22.7			21.4			23.5			3.4			3.1			3.5
Expected return on plan assets (a)	(28.1		)	(32.6		)	(30.8		)	(3.6		)	(4.4		)	(4.3		)
Amortization of prior service credit (b)	(0.2		)	(0.2		)	(0.2		)	—			—			—
Amortization of actuarial loss (c)	15.7			14.9			16.1			1.5			1.3			2.0
		$16.1			$10.9			$15.9			$2.6			$1.7			$3.3

WPL	Defined Benefit Pension Plans									OPEB Plans
	2019			2018			2017			2019			2018			2017
Service cost		$3.5			$4.4			$4.9			$1.3			$1.6			$1.9
Interest cost	21.5			20.2			21.8			3.3			3.1			3.4
Expected return on plan assets (a)	(26.2		)	(30.4		)	(28.5		)	(0.6		)	(0.6		)	(0.8		)
Amortization of prior service cost (credit) (b)	(0.2		)	(0.1		)	0.1			(0.2		)	(0.2		)	(0.2		)
Amortization of actuarial loss (c)	17.6			17.2			18.5			1.6			2.0			1.6
		$16.2			$11.3			$16.8			$5.4			$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	2019			2018			2019			2018
Change in benefit obligation:
Net benefit obligation at January 1		$1,175.0			$1,303.1			$206.1			$222.3
Service cost	9.7			12.1			3.3			4.2
Interest cost	49.8			46.8			8.5			7.7
Plan participants’ contributions	—			—			3.4			3.1
Actuarial (gain) loss	124.6			(96.2		)	13.6			(8.2		)
Gross benefits paid	(79.4		)	(90.8		)	(21.3		)	(23.0		)
Net benefit obligation at December 31	1,279.7			1,175.0			213.6			206.1
Change in plan assets:
Fair value of plan assets at January 1	808.6			950.7			99.1			111.1
Actual return on plan assets	168.1			(57.8		)	14.6			(2.6		)
Employer contributions	33.1			6.5			9.1			10.5
Plan participants’ contributions	—			—			3.4			3.1
Gross benefits paid	(79.4		)	(90.8		)	(21.3		)	(23.0		)
Fair value of plan assets at December 31	930.4			808.6			104.9			99.1
Under funded status at December 31		($349.3	)		($366.4	)		($108.7	)		($107.0	)

	Defined Benefit Pension Plans						OPEB Plans
Alliant Energy	2019			2018			2019			2018
Amounts recognized on the balance sheets consist of:
Non-current assets		$—			$—			$9.8			$7.5
Current liabilities	(14.3		)	(2.3		)	(8.1		)	(9.6		)
Pension and other benefit obligations	(335.0		)	(364.1		)	(110.4		)	(104.9		)
Net amounts recognized at December 31		($349.3	)		($366.4	)		($108.7	)		($107.0	)
Amounts recognized in Regulatory Assets consist of:
Net actuarial loss		$485.3			$505.2			$45.2			$44.5
Prior service credit	(5.1		)	(5.8		)	(0.9		)	(1.1		)
		$480.2			$499.4			$44.3			$43.4

	Defined Benefit Pension Plans						OPEB Plans
IPL	2019			2018			2019			2018
Change in benefit obligation:
Net benefit obligation at January 1		$533.9			$592.9			$82.5			$89.4
Service cost	6.0			7.4			1.3			1.7
Interest cost	22.7			21.4			3.4			3.1
Plan participants’ contributions	—			—			1.3			1.0
Actuarial (gain) loss	55.9			(44.4		)	5.7			(4.3		)
Gross benefits paid	(37.3		)	(43.4		)	(8.5		)	(8.4		)
Net benefit obligation at December 31	581.2			533.9			85.7			82.5
Change in plan assets:
Fair value of plan assets at January 1	377.8			443.7			66.7			72.9
Actual return on plan assets	78.9			(26.8		)	10.1			(1.4		)
Employer contributions	16.6			4.3			2.3			2.6
Plan participants’ contributions	—			—			1.3			1.0
Gross benefits paid	(37.3		)	(43.4		)	(8.5		)	(8.4		)
Fair value of plan assets at December 31	436.0			377.8			71.9			66.7
Under funded status at December 31		($145.2	)		($156.1	)		($13.8	)		($15.8	)

	Defined Benefit Pension Plans						OPEB Plans
IPL	2019			2018			2019			2018
Amounts recognized on the balance sheets consist of:
Non-current assets		$—			$—			$6.6			$4.7
Current liabilities	(0.5		)	(0.6		)	(1.8		)	(1.9		)
Pension and other benefit obligations	(144.7		)	(155.5		)	(18.6		)	(18.6		)
Net amounts recognized at December 31		($145.2	)		($156.1	)		($13.8	)		($15.8	)
Amounts recognized in Regulatory Assets consist of:
Net actuarial loss		$208.2			$218.8			$16.6			$18.8
Prior service credit	(1.7		)	(1.8		)	—			—
		$206.5			$217.0			$16.6			$18.8

	Defined Benefit Pension Plans						OPEB Plans
WPL	2019			2018			2019			2018
Change in benefit obligation:
Net benefit obligation at January 1		$506.6			$559.8			$83.2			$90.4
Service cost	3.5			4.4			1.3			1.6
Interest cost	21.5			20.2			3.3			3.1
Plan participants’ contributions	—			—			1.5			1.4
Actuarial (gain) loss	53.8			(40.0		)	5.0			(2.5		)
Gross benefits paid	(35.3		)	(37.8		)	(9.0		)	(10.8		)
Net benefit obligation at December 31	550.1			506.6			85.3			83.2
Change in plan assets:
Fair value of plan assets at January 1	352.2			415.0			16.7			18.7
Actual return on plan assets	73.4			(25.1		)	1.7			(0.1		)
Employer contributions	15.7			0.1			6.2			7.5
Plan participants’ contributions	—			—			1.5			1.4
Gross benefits paid	(35.3		)	(37.8		)	(9.0		)	(10.8		)
Fair value of plan assets at December 31	406.0			352.2			17.1			16.7
Under funded status at December 31		($144.1	)		($154.4	)		($68.2	)		($66.5	)

	Defined Benefit Pension Plans						OPEB Plans
WPL	2019			2018			2019			2018
Amounts recognized on the balance sheets consist of:
Non-current assets		$—			$—			$3.2			$2.8
Current liabilities	(0.1		)	(0.1		)	(6.0		)	(7.4		)
Pension and other benefit obligations	(144.0		)	(154.3		)	(65.4		)	(61.9		)
Net amounts recognized at December 31		($144.1	)		($154.4	)		($68.2	)		($66.5	)
Amounts recognized in Regulatory Assets consist of:
Net actuarial loss		$212.0			$223.0			$22.2			$19.9
Prior service credit	(1.2		)	(1.3		)	(0.9		)	(1.1		)
		$210.8			$221.7			$21.3			$18.8

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	2019		2018		2019		2018
Accumulated benefit obligations		$1,234.4		$1,139.9		$213.6		$206.1
Plans with accumulated benefit obligations in excess of plan assets:
Accumulated benefit obligations	1,234.4		1,139.9		213.6		206.1
Fair value of plan assets	930.4		808.6		104.9		99.1
Plans with projected benefit obligations in excess of plan assets:
Projected benefit obligations	1,279.7		1,175.0		N/A		N/A
Fair value of plan assets	930.4		808.6		N/A		N/A

	Defined Benefit Pension Plans				OPEB Plans
IPL	2019		2018		2019		2018
Accumulated benefit obligations		$557.8		$514.3		$85.7		$82.5
Plans with accumulated benefit obligations in excess of plan assets:
Accumulated benefit obligations	557.8		514.3		85.7		82.5
Fair value of plan assets	436.0		377.8		71.9		66.7
Plans with projected benefit obligations in excess of plan assets:
Projected benefit obligations	581.2		533.9		N/A		N/A
Fair value of plan assets	436.0		377.8		N/A		N/A

	Defined Benefit Pension Plans				OPEB Plans
WPL	2019		2018		2019		2018
Accumulated benefit obligations		$535.9		$494.8		$85.3		$83.2
Plans with accumulated benefit obligations in excess of plan assets:
Accumulated benefit obligations	535.9		494.8		85.3		83.2
Fair value of plan assets	406.0		352.2		17.1		16.7
Plans with projected benefit obligations in excess of plan assets:
Projected benefit obligations	550.1		506.6		N/A		N/A
Fair value of plan assets	406.0		352.2		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
	2019		2018		2019		2018
Regulatory assets		$39.4		$38.2		$29.0		$27.7

Estimated Future Employer Contributions

Estimated funding for the qualified and non-qualified defined benefit pension and OPEB plans for 2020 is as follows (in millions):

	Alliant Energy		IPL		WPL
Defined benefit pension plans (a)		$59.8		$19.4		$21.8
OPEB plans	8.1		1.8		6.0

(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	2020		2021		2022		2023		2024		2025 - 2029
Defined benefit pension benefits		$86.4		$74.5		$76.6		$77.5		$78.2		$390.2
OPEB	17.7		17.7		17.5		17.1		16.8		76.6
		$104.1		$92.2		$94.1		$94.6		$95.0		$466.8

IPL	2020		2021		2022		2023		2024		2025 - 2029
Defined benefit pension benefits		$35.1		$35.3		$36.6		$37.7		$36.6		$182.5
OPEB	7.2		7.1		7.1		7.0		6.9		30.6
		$42.3		$42.4		$43.7		$44.7		$43.5		$213.1

WPL	2020		2021		2022		2023		2024		2025 - 2029
Defined benefit pension benefits		$32.0		$32.0		$32.1		$32.4		$33.1		$165.2
OPEB	7.3		7.4		7.1		6.8		6.7		30.2
		$39.3		$39.4		$39.2		$39.2		$39.8		$195.4

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
	2019		2018		2017		2019		2018		2017		2019		2018		2017
Compensation expense		$26.0		$17.0		$15.1		$14.5		$9.4		$8.3		$10.3		$6.9		$6.4
Income tax benefits	7.3		4.9		6.2		4.2		2.8		3.4		2.8		1.9		2.6

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):

	2019		2018
Carrying value		$10.0		$9.8
Fair market value	20.9		16.2

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	2019				2018				2017				2019	2018	2017
Discount rate for benefit obligations	3.48%				4.34%				3.66%				3.40%	4.24%	3.53%
Discount rate for net periodic cost	4.34%				3.66%				4.19%				4.24%	3.53%	3.98%
Expected rate of return on plan assets	7.60%				7.60%				7.60%				5.44%	5.44%	5.80%
Interest crediting rate for Alliant Energy Cash Balance Pension Plan	5.52%				5.04%				4.64%				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

	Qualified Defined Benefit Pension Plan			OPEB Plans
IPL	2019	2018	2017	2019	2018	2017
Discount rate for benefit obligations	3.51%	4.35%	3.68%	3.39%	4.23%	3.51%
Discount rate for net periodic cost	4.35%	3.68%	4.22%	4.23%	3.51%	3.95%
Expected rate of return on plan assets	7.60%	7.60%	7.60%	5.60%	5.60%	6.20%
Rate of compensation increase	3.65%	3.65%	3.65%	N/A	N/A	N/A

	Qualified Defined Benefit Pension Plan			OPEB Plans
WPL	2019	2018	2017	2019	2018	2017
Discount rate for benefit obligations	3.50%	4.35%	3.69%	3.39%	4.23%	3.51%
Discount rate for net periodic cost	4.35%	3.69%	4.23%	4.23%	3.51%	3.96%
Expected rate of return on plan assets	7.60%	7.60%	7.60%	3.81%	3.84%	3.50%
Rate of compensation increase	3.65%	3.65%	3.65%	N/A	N/A	N/A

Net Periodic Benefit Costs

The components of net periodic benefit costs for sponsored defined benefit pension and OPEB plans are included 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
	2019			2018			2017			2019			2018			2017
Service cost		$9.7			$12.1			$12.5			$3.3			$4.2			$5.0
Interest cost	49.8			46.8			51.0			8.5			7.7			8.6
Expected return on plan assets (a)	(60.1		)	(69.7		)	(65.5		)	(5.0		)	(6.0		)	(6.1		)
Amortization of prior service credit (b)	(0.7		)	(0.7		)	(0.4		)	(0.2		)	(0.2		)	(0.2		)
Amortization of actuarial loss (c)	36.4			35.2			37.6			3.3			3.4			3.8
Settlement losses (d)	—			—			0.9			—			—			—
		$35.1			$23.7			$36.1			$9.9			$9.1			$11.1

IPL	Defined Benefit Pension Plans									OPEB Plans
	2019			2018			2017			2019			2018			2017
Service cost		$6.0			$7.4			$7.3			$1.3			$1.7			$2.1
Interest cost	22.7			21.4			23.5			3.4			3.1			3.5
Expected return on plan assets (a)	(28.1		)	(32.6		)	(30.8		)	(3.6		)	(4.4		)	(4.3		)
Amortization of prior service credit (b)	(0.2		)	(0.2		)	(0.2		)	—			—			—
Amortization of actuarial loss (c)	15.7			14.9			16.1			1.5			1.3			2.0
		$16.1			$10.9			$15.9			$2.6			$1.7			$3.3

WPL	Defined Benefit Pension Plans									OPEB Plans
	2019			2018			2017			2019			2018			2017
Service cost		$3.5			$4.4			$4.9			$1.3			$1.6			$1.9
Interest cost	21.5			20.2			21.8			3.3			3.1			3.4
Expected return on plan assets (a)	(26.2		)	(30.4		)	(28.5		)	(0.6		)	(0.6		)	(0.8		)
Amortization of prior service cost (credit) (b)	(0.2		)	(0.1		)	0.1			(0.2		)	(0.2		)	(0.2		)
Amortization of actuarial loss (c)	17.6			17.2			18.5			1.6			2.0			1.6
		$16.2			$11.3			$16.8			$5.4			$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	2019			2018			2019			2018
Change in benefit obligation:
Net benefit obligation at January 1		$1,175.0			$1,303.1			$206.1			$222.3
Service cost	9.7			12.1			3.3			4.2
Interest cost	49.8			46.8			8.5			7.7
Plan participants’ contributions	—			—			3.4			3.1
Actuarial (gain) loss	124.6			(96.2		)	13.6			(8.2		)
Gross benefits paid	(79.4		)	(90.8		)	(21.3		)	(23.0		)
Net benefit obligation at December 31	1,279.7			1,175.0			213.6			206.1
Change in plan assets:
Fair value of plan assets at January 1	808.6			950.7			99.1			111.1
Actual return on plan assets	168.1			(57.8		)	14.6			(2.6		)
Employer contributions	33.1			6.5			9.1			10.5
Plan participants’ contributions	—			—			3.4			3.1
Gross benefits paid	(79.4		)	(90.8		)	(21.3		)	(23.0		)
Fair value of plan assets at December 31	930.4			808.6			104.9			99.1
Under funded status at December 31		($349.3	)		($366.4	)		($108.7	)		($107.0	)

	Defined Benefit Pension Plans						OPEB Plans
Alliant Energy	2019			2018			2019			2018
Amounts recognized on the balance sheets consist of:
Non-current assets		$—			$—			$9.8			$7.5
Current liabilities	(14.3		)	(2.3		)	(8.1		)	(9.6		)
Pension and other benefit obligations	(335.0		)	(364.1		)	(110.4		)	(104.9		)
Net amounts recognized at December 31		($349.3	)		($366.4	)		($108.7	)		($107.0	)
Amounts recognized in Regulatory Assets consist of:
Net actuarial loss		$485.3			$505.2			$45.2			$44.5
Prior service credit	(5.1		)	(5.8		)	(0.9		)	(1.1		)
		$480.2			$499.4			$44.3			$43.4

	Defined Benefit Pension Plans						OPEB Plans
IPL	2019			2018			2019			2018
Change in benefit obligation:
Net benefit obligation at January 1		$533.9			$592.9			$82.5			$89.4
Service cost	6.0			7.4			1.3			1.7
Interest cost	22.7			21.4			3.4			3.1
Plan participants’ contributions	—			—			1.3			1.0
Actuarial (gain) loss	55.9			(44.4		)	5.7			(4.3		)
Gross benefits paid	(37.3		)	(43.4		)	(8.5		)	(8.4		)
Net benefit obligation at December 31	581.2			533.9			85.7			82.5
Change in plan assets:
Fair value of plan assets at January 1	377.8			443.7			66.7			72.9
Actual return on plan assets	78.9			(26.8		)	10.1			(1.4		)
Employer contributions	16.6			4.3			2.3			2.6
Plan participants’ contributions	—			—			1.3			1.0
Gross benefits paid	(37.3		)	(43.4		)	(8.5		)	(8.4		)
Fair value of plan assets at December 31	436.0			377.8			71.9			66.7
Under funded status at December 31		($145.2	)		($156.1	)		($13.8	)		($15.8	)

	Defined Benefit Pension Plans						OPEB Plans
IPL	2019			2018			2019			2018
Amounts recognized on the balance sheets consist of:
Non-current assets		$—			$—			$6.6			$4.7
Current liabilities	(0.5		)	(0.6		)	(1.8		)	(1.9		)
Pension and other benefit obligations	(144.7		)	(155.5		)	(18.6		)	(18.6		)
Net amounts recognized at December 31		($145.2	)		($156.1	)		($13.8	)		($15.8	)
Amounts recognized in Regulatory Assets consist of:
Net actuarial loss		$208.2			$218.8			$16.6			$18.8
Prior service credit	(1.7		)	(1.8		)	—			—
		$206.5			$217.0			$16.6			$18.8

	Defined Benefit Pension Plans						OPEB Plans
WPL	2019			2018			2019			2018
Change in benefit obligation:
Net benefit obligation at January 1		$506.6			$559.8			$83.2			$90.4
Service cost	3.5			4.4			1.3			1.6
Interest cost	21.5			20.2			3.3			3.1
Plan participants’ contributions	—			—			1.5			1.4
Actuarial (gain) loss	53.8			(40.0		)	5.0			(2.5		)
Gross benefits paid	(35.3		)	(37.8		)	(9.0		)	(10.8		)
Net benefit obligation at December 31	550.1			506.6			85.3			83.2
Change in plan assets:
Fair value of plan assets at January 1	352.2			415.0			16.7			18.7
Actual return on plan assets	73.4			(25.1		)	1.7			(0.1		)
Employer contributions	15.7			0.1			6.2			7.5
Plan participants’ contributions	—			—			1.5			1.4
Gross benefits paid	(35.3		)	(37.8		)	(9.0		)	(10.8		)
Fair value of plan assets at December 31	406.0			352.2			17.1			16.7
Under funded status at December 31		($144.1	)		($154.4	)		($68.2	)		($66.5	)

	Defined Benefit Pension Plans						OPEB Plans
WPL	2019			2018			2019			2018
Amounts recognized on the balance sheets consist of:
Non-current assets		$—			$—			$3.2			$2.8
Current liabilities	(0.1		)	(0.1		)	(6.0		)	(7.4		)
Pension and other benefit obligations	(144.0		)	(154.3		)	(65.4		)	(61.9		)
Net amounts recognized at December 31		($144.1	)		($154.4	)		($68.2	)		($66.5	)
Amounts recognized in Regulatory Assets consist of:
Net actuarial loss		$212.0			$223.0			$22.2			$19.9
Prior service credit	(1.2		)	(1.3		)	(0.9		)	(1.1		)
		$210.8			$221.7			$21.3			$18.8

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	2019		2018		2019		2018
Accumulated benefit obligations		$1,234.4		$1,139.9		$213.6		$206.1
Plans with accumulated benefit obligations in excess of plan assets:
Accumulated benefit obligations	1,234.4		1,139.9		213.6		206.1
Fair value of plan assets	930.4		808.6		104.9		99.1
Plans with projected benefit obligations in excess of plan assets:
Projected benefit obligations	1,279.7		1,175.0		N/A		N/A
Fair value of plan assets	930.4		808.6		N/A		N/A

	Defined Benefit Pension Plans				OPEB Plans
IPL	2019		2018		2019		2018
Accumulated benefit obligations		$557.8		$514.3		$85.7		$82.5
Plans with accumulated benefit obligations in excess of plan assets:
Accumulated benefit obligations	557.8		514.3		85.7		82.5
Fair value of plan assets	436.0		377.8		71.9		66.7
Plans with projected benefit obligations in excess of plan assets:
Projected benefit obligations	581.2		533.9		N/A		N/A
Fair value of plan assets	436.0		377.8		N/A		N/A

	Defined Benefit Pension Plans				OPEB Plans
WPL	2019		2018		2019		2018
Accumulated benefit obligations		$535.9		$494.8		$85.3		$83.2
Plans with accumulated benefit obligations in excess of plan assets:
Accumulated benefit obligations	535.9		494.8		85.3		83.2
Fair value of plan assets	406.0		352.2		17.1		16.7
Plans with projected benefit obligations in excess of plan assets:
Projected benefit obligations	550.1		506.6		N/A		N/A
Fair value of plan assets	406.0		352.2		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
	2019		2018		2019		2018
Regulatory assets		$39.4		$38.2		$29.0		$27.7

Estimated Future Employer Contributions

Estimated funding for the qualified and non-qualified defined benefit pension and OPEB plans for 2020 is as follows (in millions):

	Alliant Energy		IPL		WPL
Defined benefit pension plans (a)		$59.8		$19.4		$21.8
OPEB plans	8.1		1.8		6.0

(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	2020		2021		2022		2023		2024		2025 - 2029
Defined benefit pension benefits		$86.4		$74.5		$76.6		$77.5		$78.2		$390.2
OPEB	17.7		17.7		17.5		17.1		16.8		76.6
		$104.1		$92.2		$94.1		$94.6		$95.0		$466.8

IPL	2020		2021		2022		2023		2024		2025 - 2029
Defined benefit pension benefits		$35.1		$35.3		$36.6		$37.7		$36.6		$182.5
OPEB	7.2		7.1		7.1		7.0		6.9		30.6
		$42.3		$42.4		$43.7		$44.7		$43.5		$213.1

WPL	2020		2021		2022		2023		2024		2025 - 2029
Defined benefit pension benefits		$32.0		$32.0		$32.1		$32.4		$33.1		$165.2
OPEB	7.3		7.4		7.1		6.8		6.7		30.2
		$39.3		$39.4		$39.2		$39.2		$39.8		$195.4

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
	2019		2018		2017		2019		2018		2017		2019		2018		2017
Compensation expense		$26.0		$17.0		$15.1		$14.5		$9.4		$8.3		$10.3		$6.9		$6.4
Income tax benefits	7.3		4.9		6.2		4.2		2.8		3.4		2.8		1.9		2.6

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	2019				2018				2017				2019	2018	2017
Discount rate for benefit obligations	3.48%				4.34%				3.66%				3.40%	4.24%	3.53%
Discount rate for net periodic cost	4.34%				3.66%				4.19%				4.24%	3.53%	3.98%
Expected rate of return on plan assets	7.60%				7.60%				7.60%				5.44%	5.44%	5.80%
Interest crediting rate for Alliant Energy Cash Balance Pension Plan	5.52%				5.04%				4.64%				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

	Qualified Defined Benefit Pension Plan			OPEB Plans
IPL	2019	2018	2017	2019	2018	2017
Discount rate for benefit obligations	3.51%	4.35%	3.68%	3.39%	4.23%	3.51%
Discount rate for net periodic cost	4.35%	3.68%	4.22%	4.23%	3.51%	3.95%
Expected rate of return on plan assets	7.60%	7.60%	7.60%	5.60%	5.60%	6.20%
Rate of compensation increase	3.65%	3.65%	3.65%	N/A	N/A	N/A

	Qualified Defined Benefit Pension Plan			OPEB Plans
WPL	2019	2018	2017	2019	2018	2017
Discount rate for benefit obligations	3.50%	4.35%	3.69%	3.39%	4.23%	3.51%
Discount rate for net periodic cost	4.35%	3.69%	4.23%	4.23%	3.51%	3.96%
Expected rate of return on plan assets	7.60%	7.60%	7.60%	3.81%	3.84%	3.50%
Rate of compensation increase	3.65%	3.65%	3.65%	N/A	N/A	N/A

Net Periodic Benefit Costs

The components of net periodic benefit costs for sponsored defined benefit pension and OPEB plans are included 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
	2019			2018			2017			2019			2018			2017
Service cost		$9.7			$12.1			$12.5			$3.3			$4.2			$5.0
Interest cost	49.8			46.8			51.0			8.5			7.7			8.6
Expected return on plan assets (a)	(60.1		)	(69.7		)	(65.5		)	(5.0		)	(6.0		)	(6.1		)
Amortization of prior service credit (b)	(0.7		)	(0.7		)	(0.4		)	(0.2		)	(0.2		)	(0.2		)
Amortization of actuarial loss (c)	36.4			35.2			37.6			3.3			3.4			3.8
Settlement losses (d)	—			—			0.9			—			—			—
		$35.1			$23.7			$36.1			$9.9			$9.1			$11.1

IPL	Defined Benefit Pension Plans									OPEB Plans
	2019			2018			2017			2019			2018			2017
Service cost		$6.0			$7.4			$7.3			$1.3			$1.7			$2.1
Interest cost	22.7			21.4			23.5			3.4			3.1			3.5
Expected return on plan assets (a)	(28.1		)	(32.6		)	(30.8		)	(3.6		)	(4.4		)	(4.3		)
Amortization of prior service credit (b)	(0.2		)	(0.2		)	(0.2		)	—			—			—
Amortization of actuarial loss (c)	15.7			14.9			16.1			1.5			1.3			2.0
		$16.1			$10.9			$15.9			$2.6			$1.7			$3.3

WPL	Defined Benefit Pension Plans									OPEB Plans
	2019			2018			2017			2019			2018			2017
Service cost		$3.5			$4.4			$4.9			$1.3			$1.6			$1.9
Interest cost	21.5			20.2			21.8			3.3			3.1			3.4
Expected return on plan assets (a)	(26.2		)	(30.4		)	(28.5		)	(0.6		)	(0.6		)	(0.8		)
Amortization of prior service cost (credit) (b)	(0.2		)	(0.1		)	0.1			(0.2		)	(0.2		)	(0.2		)
Amortization of actuarial loss (c)	17.6			17.2			18.5			1.6			2.0			1.6
		$16.2			$11.3			$16.8			$5.4			$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	2019			2018			2019			2018
Change in benefit obligation:
Net benefit obligation at January 1		$1,175.0			$1,303.1			$206.1			$222.3
Service cost	9.7			12.1			3.3			4.2
Interest cost	49.8			46.8			8.5			7.7
Plan participants’ contributions	—			—			3.4			3.1
Actuarial (gain) loss	124.6			(96.2		)	13.6			(8.2		)
Gross benefits paid	(79.4		)	(90.8		)	(21.3		)	(23.0		)
Net benefit obligation at December 31	1,279.7			1,175.0			213.6			206.1
Change in plan assets:
Fair value of plan assets at January 1	808.6			950.7			99.1			111.1
Actual return on plan assets	168.1			(57.8		)	14.6			(2.6		)
Employer contributions	33.1			6.5			9.1			10.5
Plan participants’ contributions	—			—			3.4			3.1
Gross benefits paid	(79.4		)	(90.8		)	(21.3		)	(23.0		)
Fair value of plan assets at December 31	930.4			808.6			104.9			99.1
Under funded status at December 31		($349.3	)		($366.4	)		($108.7	)		($107.0	)

	Defined Benefit Pension Plans						OPEB Plans
Alliant Energy	2019			2018			2019			2018
Amounts recognized on the balance sheets consist of:
Non-current assets		$—			$—			$9.8			$7.5
Current liabilities	(14.3		)	(2.3		)	(8.1		)	(9.6		)
Pension and other benefit obligations	(335.0		)	(364.1		)	(110.4		)	(104.9		)
Net amounts recognized at December 31		($349.3	)		($366.4	)		($108.7	)		($107.0	)
Amounts recognized in Regulatory Assets consist of:
Net actuarial loss		$485.3			$505.2			$45.2			$44.5
Prior service credit	(5.1		)	(5.8		)	(0.9		)	(1.1		)
		$480.2			$499.4			$44.3			$43.4

	Defined Benefit Pension Plans						OPEB Plans
IPL	2019			2018			2019			2018
Change in benefit obligation:
Net benefit obligation at January 1		$533.9			$592.9			$82.5			$89.4
Service cost	6.0			7.4			1.3			1.7
Interest cost	22.7			21.4			3.4			3.1
Plan participants’ contributions	—			—			1.3			1.0
Actuarial (gain) loss	55.9			(44.4		)	5.7			(4.3		)
Gross benefits paid	(37.3		)	(43.4		)	(8.5		)	(8.4		)
Net benefit obligation at December 31	581.2			533.9			85.7			82.5
Change in plan assets:
Fair value of plan assets at January 1	377.8			443.7			66.7			72.9
Actual return on plan assets	78.9			(26.8		)	10.1			(1.4		)
Employer contributions	16.6			4.3			2.3			2.6
Plan participants’ contributions	—			—			1.3			1.0
Gross benefits paid	(37.3		)	(43.4		)	(8.5		)	(8.4		)
Fair value of plan assets at December 31	436.0			377.8			71.9			66.7
Under funded status at December 31		($145.2	)		($156.1	)		($13.8	)		($15.8	)

	Defined Benefit Pension Plans						OPEB Plans
IPL	2019			2018			2019			2018
Amounts recognized on the balance sheets consist of:
Non-current assets		$—			$—			$6.6			$4.7
Current liabilities	(0.5		)	(0.6		)	(1.8		)	(1.9		)
Pension and other benefit obligations	(144.7		)	(155.5		)	(18.6		)	(18.6		)
Net amounts recognized at December 31		($145.2	)		($156.1	)		($13.8	)		($15.8	)
Amounts recognized in Regulatory Assets consist of:
Net actuarial loss		$208.2			$218.8			$16.6			$18.8
Prior service credit	(1.7		)	(1.8		)	—			—
		$206.5			$217.0			$16.6			$18.8

	Defined Benefit Pension Plans						OPEB Plans
WPL	2019			2018			2019			2018
Change in benefit obligation:
Net benefit obligation at January 1		$506.6			$559.8			$83.2			$90.4
Service cost	3.5			4.4			1.3			1.6
Interest cost	21.5			20.2			3.3			3.1
Plan participants’ contributions	—			—			1.5			1.4
Actuarial (gain) loss	53.8			(40.0		)	5.0			(2.5		)
Gross benefits paid	(35.3		)	(37.8		)	(9.0		)	(10.8		)
Net benefit obligation at December 31	550.1			506.6			85.3			83.2
Change in plan assets:
Fair value of plan assets at January 1	352.2			415.0			16.7			18.7
Actual return on plan assets	73.4			(25.1		)	1.7			(0.1		)
Employer contributions	15.7			0.1			6.2			7.5
Plan participants’ contributions	—			—			1.5			1.4
Gross benefits paid	(35.3		)	(37.8		)	(9.0		)	(10.8		)
Fair value of plan assets at December 31	406.0			352.2			17.1			16.7
Under funded status at December 31		($144.1	)		($154.4	)		($68.2	)		($66.5	)

	Defined Benefit Pension Plans						OPEB Plans
WPL	2019			2018			2019			2018
Amounts recognized on the balance sheets consist of:
Non-current assets		$—			$—			$3.2			$2.8
Current liabilities	(0.1		)	(0.1		)	(6.0		)	(7.4		)
Pension and other benefit obligations	(144.0		)	(154.3		)	(65.4		)	(61.9		)
Net amounts recognized at December 31		($144.1	)		($154.4	)		($68.2	)		($66.5	)
Amounts recognized in Regulatory Assets consist of:
Net actuarial loss		$212.0			$223.0			$22.2			$19.9
Prior service credit	(1.2		)	(1.3		)	(0.9		)	(1.1		)
		$210.8			$221.7			$21.3			$18.8

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	2019		2018		2019		2018
Accumulated benefit obligations		$1,234.4		$1,139.9		$213.6		$206.1
Plans with accumulated benefit obligations in excess of plan assets:
Accumulated benefit obligations	1,234.4		1,139.9		213.6		206.1
Fair value of plan assets	930.4		808.6		104.9		99.1
Plans with projected benefit obligations in excess of plan assets:
Projected benefit obligations	1,279.7		1,175.0		N/A		N/A
Fair value of plan assets	930.4		808.6		N/A		N/A

	Defined Benefit Pension Plans				OPEB Plans
IPL	2019		2018		2019		2018
Accumulated benefit obligations		$557.8		$514.3		$85.7		$82.5
Plans with accumulated benefit obligations in excess of plan assets:
Accumulated benefit obligations	557.8		514.3		85.7		82.5
Fair value of plan assets	436.0		377.8		71.9		66.7
Plans with projected benefit obligations in excess of plan assets:
Projected benefit obligations	581.2		533.9		N/A		N/A
Fair value of plan assets	436.0		377.8		N/A		N/A

	Defined Benefit Pension Plans				OPEB Plans
WPL	2019		2018		2019		2018
Accumulated benefit obligations		$535.9		$494.8		$85.3		$83.2
Plans with accumulated benefit obligations in excess of plan assets:
Accumulated benefit obligations	535.9		494.8		85.3		83.2
Fair value of plan assets	406.0		352.2		17.1		16.7
Plans with projected benefit obligations in excess of plan assets:
Projected benefit obligations	550.1		506.6		N/A		N/A
Fair value of plan assets	406.0		352.2		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
	2019		2018		2019		2018
Regulatory assets		$39.4		$38.2		$29.0		$27.7

Estimated Future Employer Contributions

Estimated funding for the qualified and non-qualified defined benefit pension and OPEB plans for 2020 is as follows (in millions):

	Alliant Energy		IPL		WPL
Defined benefit pension plans (a)		$59.8		$19.4		$21.8
OPEB plans	8.1		1.8		6.0

(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	2020		2021		2022		2023		2024		2025 - 2029
Defined benefit pension benefits		$86.4		$74.5		$76.6		$77.5		$78.2		$390.2
OPEB	17.7		17.7		17.5		17.1		16.8		76.6
		$104.1		$92.2		$94.1		$94.6		$95.0		$466.8

IPL	2020		2021		2022		2023		2024		2025 - 2029
Defined benefit pension benefits		$35.1		$35.3		$36.6		$37.7		$36.6		$182.5
OPEB	7.2		7.1		7.1		7.0		6.9		30.6
		$42.3		$42.4		$43.7		$44.7		$43.5		$213.1

WPL	2020		2021		2022		2023		2024		2025 - 2029
Defined benefit pension benefits		$32.0		$32.0		$32.1		$32.4		$33.1		$165.2
OPEB	7.3		7.4		7.1		6.8		6.7		30.2
		$39.3		$39.4		$39.2		$39.2		$39.8		$195.4

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
	2019		2018		2017		2019		2018		2017		2019		2018		2017
Compensation expense		$26.0		$17.0		$15.1		$14.5		$9.4		$8.3		$10.3		$6.9		$6.4
Income tax benefits	7.3		4.9		6.2		4.2		2.8		3.4		2.8		1.9		2.6

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, 2019, 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%	5%
Equity securities - U.S.	6	%	-	56%	25%
Equity securities - international	14	%	-	34%	22%
Global asset securities	5	%	-	15%	9%
Risk parity securities	5	%	-	15%	10%
Fixed income securities	20	%	-	40%	29%

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

	2019									2018
	Fair			Level		Level		Level		Fair			Level		Level		Level
Alliant Energy	Value			1		2		3		Value			1		2		3
Cash and equivalents		$45.7			$3.7		$42.0		$—		$36.4			$3.0		$33.4		$—
Equity securities - U.S.	160.6			160.6		—		—		130.2			130.2		—		—
Equity securities - international	135.9			135.9		—		—		116.0			116.0		—		—
Global asset securities	47.2			47.2		—		—		42.1			42.1		—		—
Fixed income securities	130.7			58.0		72.7		—		127.8			52.5		75.3		—
Total assets in fair value hierarchy	520.1				$405.4		$114.7		$—	452.5				$343.8		$108.7		$—
Assets measured at net asset value	410.1									355.4
Accrued investment income	0.9									1.2
Due to brokers, net (pending trades with brokers)	(0.7		)							(0.5		)
Total pension plan assets		$930.4									$808.6

	2019									2018
	Fair			Level		Level		Level		Fair			Level		Level		Level
IPL	Value			1		2		3		Value			1		2		3
Cash and equivalents		$21.4			$1.7		$19.7		$—		$17.0			$1.4		$15.6		$—
Equity securities - U.S.	75.2			75.2		—		—		60.8			60.8		—		—
Equity securities - international	63.7			63.7		—		—		54.2			54.2		—		—
Global asset securities	22.1			22.1		—		—		19.7			19.7		—		—
Fixed income securities	61.3			27.2		34.1		—		59.7			24.5		35.2		—
Total assets in fair value hierarchy	243.7				$189.9		$53.8		$—	211.4				$160.6		$50.8		$—
Assets measured at net asset value	192.2									166.1
Accrued investment income	0.4									0.6
Due to brokers, net (pending trades with brokers)	(0.3		)							(0.3		)
Total pension plan assets		$436.0									$377.8

	2019									2018
	Fair			Level		Level		Level		Fair			Level		Level		Level
WPL	Value			1		2		3		Value			1		2		3
Cash and equivalents		$19.9			$1.6		$18.3		$—		$15.9			$1.3		$14.6		$—
Equity securities - U.S.	70.1			70.1		—		—		56.7			56.7		—		—
Equity securities - international	59.3			59.3		—		—		50.5			50.5		—		—
Global asset securities	20.6			20.6		—		—		18.4			18.4		—		—
Fixed income securities	57.0			25.3		31.7		—		55.6			22.8		32.8		—
Total assets in fair value hierarchy	226.9				$176.9		$50.0		$—	197.1				$149.7		$47.4		$—
Assets measured at net asset value	179.0									154.8
Accrued investment income	0.4									0.5
Due to brokers, net (pending trades with brokers)	(0.3		)							(0.2		)
Total pension plan assets		$406.0									$352.2

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):

	2019									2018
	Fair			Level		Level		Level		Fair			Level		Level		Level
Alliant Energy	Value			1		2		3		Value			1		2		3
Cash and equivalents		$45.7			$3.7		$42.0		$—		$36.4			$3.0		$33.4		$—
Equity securities - U.S.	160.6			160.6		—		—		130.2			130.2		—		—
Equity securities - international	135.9			135.9		—		—		116.0			116.0		—		—
Global asset securities	47.2			47.2		—		—		42.1			42.1		—		—
Fixed income securities	130.7			58.0		72.7		—		127.8			52.5		75.3		—
Total assets in fair value hierarchy	520.1				$405.4		$114.7		$—	452.5				$343.8		$108.7		$—
Assets measured at net asset value	410.1									355.4
Accrued investment income	0.9									1.2
Due to brokers, net (pending trades with brokers)	(0.7		)							(0.5		)
Total pension plan assets		$930.4									$808.6

	2019									2018
	Fair			Level		Level		Level		Fair			Level		Level		Level
IPL	Value			1		2		3		Value			1		2		3
Cash and equivalents		$21.4			$1.7		$19.7		$—		$17.0			$1.4		$15.6		$—
Equity securities - U.S.	75.2			75.2		—		—		60.8			60.8		—		—
Equity securities - international	63.7			63.7		—		—		54.2			54.2		—		—
Global asset securities	22.1			22.1		—		—		19.7			19.7		—		—
Fixed income securities	61.3			27.2		34.1		—		59.7			24.5		35.2		—
Total assets in fair value hierarchy	243.7				$189.9		$53.8		$—	211.4				$160.6		$50.8		$—
Assets measured at net asset value	192.2									166.1
Accrued investment income	0.4									0.6
Due to brokers, net (pending trades with brokers)	(0.3		)							(0.3		)
Total pension plan assets		$436.0									$377.8

	2019									2018
	Fair			Level		Level		Level		Fair			Level		Level		Level
WPL	Value			1		2		3		Value			1		2		3
Cash and equivalents		$19.9			$1.6		$18.3		$—		$15.9			$1.3		$14.6		$—
Equity securities - U.S.	70.1			70.1		—		—		56.7			56.7		—		—
Equity securities - international	59.3			59.3		—		—		50.5			50.5		—		—
Global asset securities	20.6			20.6		—		—		18.4			18.4		—		—
Fixed income securities	57.0			25.3		31.7		—		55.6			22.8		32.8		—
Total assets in fair value hierarchy	226.9				$176.9		$50.0		$—	197.1				$149.7		$47.4		$—
Assets measured at net asset value	179.0									154.8
Accrued investment income	0.4									0.5
Due to brokers, net (pending trades with brokers)	(0.3		)							(0.2		)
Total pension plan assets		$406.0									$352.2

At December 31, 2019, 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%	5%
Equity securities - U.S.	6	%	-	56%	25%
Equity securities - international	14	%	-	34%	22%
Global asset securities	5	%	-	15%	9%
Risk parity securities	5	%	-	15%	10%
Fixed income securities	20	%	-	40%	29%

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):

	2019									2018
	Fair			Level		Level		Level		Fair			Level		Level		Level
Alliant Energy	Value			1		2		3		Value			1		2		3
Cash and equivalents		$45.7			$3.7		$42.0		$—		$36.4			$3.0		$33.4		$—
Equity securities - U.S.	160.6			160.6		—		—		130.2			130.2		—		—
Equity securities - international	135.9			135.9		—		—		116.0			116.0		—		—
Global asset securities	47.2			47.2		—		—		42.1			42.1		—		—
Fixed income securities	130.7			58.0		72.7		—		127.8			52.5		75.3		—
Total assets in fair value hierarchy	520.1				$405.4		$114.7		$—	452.5				$343.8		$108.7		$—
Assets measured at net asset value	410.1									355.4
Accrued investment income	0.9									1.2
Due to brokers, net (pending trades with brokers)	(0.7		)							(0.5		)
Total pension plan assets		$930.4									$808.6

	2019									2018
	Fair			Level		Level		Level		Fair			Level		Level		Level
IPL	Value			1		2		3		Value			1		2		3
Cash and equivalents		$21.4			$1.7		$19.7		$—		$17.0			$1.4		$15.6		$—
Equity securities - U.S.	75.2			75.2		—		—		60.8			60.8		—		—
Equity securities - international	63.7			63.7		—		—		54.2			54.2		—		—
Global asset securities	22.1			22.1		—		—		19.7			19.7		—		—
Fixed income securities	61.3			27.2		34.1		—		59.7			24.5		35.2		—
Total assets in fair value hierarchy	243.7				$189.9		$53.8		$—	211.4				$160.6		$50.8		$—
Assets measured at net asset value	192.2									166.1
Accrued investment income	0.4									0.6
Due to brokers, net (pending trades with brokers)	(0.3		)							(0.3		)
Total pension plan assets		$436.0									$377.8

	2019									2018
	Fair			Level		Level		Level		Fair			Level		Level		Level
WPL	Value			1		2		3		Value			1		2		3
Cash and equivalents		$19.9			$1.6		$18.3		$—		$15.9			$1.3		$14.6		$—
Equity securities - U.S.	70.1			70.1		—		—		56.7			56.7		—		—
Equity securities - international	59.3			59.3		—		—		50.5			50.5		—		—
Global asset securities	20.6			20.6		—		—		18.4			18.4		—		—
Fixed income securities	57.0			25.3		31.7		—		55.6			22.8		32.8		—
Total assets in fair value hierarchy	226.9				$176.9		$50.0		$—	197.1				$149.7		$47.4		$—
Assets measured at net asset value	179.0									154.8
Accrued investment income	0.4									0.5
Due to brokers, net (pending trades with brokers)	(0.3		)							(0.2		)
Total pension plan assets		$406.0									$352.2

At December 31, 2019, 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%	5%
Equity securities - U.S.	6	%	-	56%	25%
Equity securities - international	14	%	-	34%	22%
Global asset securities	5	%	-	15%	9%
Risk parity securities	5	%	-	15%	10%
Fixed income securities	20	%	-	40%	29%

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, 2019, 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%	3%
Equity securities - U.S.	0	%	-	46%	25%
Equity securities - international	0	%	-	34%	2%
Fixed income securities	20	%	-	100%	70%

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

	2019								2018
	Fair		Level		Level		Level		Fair		Level		Level		Level
Alliant Energy	Value		1		2		3		Value		1		2		3
Cash and equivalents		$3.4		$3.0		$0.4		$—		$1.4		$1.1		$0.3		$—
Equity securities - U.S.	3.7		3.7		—		—		3.9		3.9		—		—
Equity securities - international	2.8		2.8		—		—		2.9		2.9		—		—
Global asset securities	0.5		0.5		—		—		0.4		0.4		—		—
Fixed income securities	68.5		67.8		0.7		—		68.2		67.5		0.7		—
Total assets in fair value hierarchy	78.9			$77.8		$1.1		$—	76.8			$75.8		$1.0		$—
Assets measured at net asset value	26.0								22.3
Total OPEB plan assets		$104.9								$99.1

	2019								2018
	Fair		Level		Level		Level		Fair		Level		Level		Level
IPL	Value		1		2		3		Value		1		2		3
Cash and equivalents		$1.5		$1.5		$—		$—		$0.7		$0.7		$—		$—
Fixed income securities	48.3		48.3		—		—		47.0		47.0		—		—
Total assets in fair value hierarchy	49.8			$49.8		$—		$—	47.7			$47.7		$—		$—
Assets measured at net asset value	22.1								19.0
Total OPEB plan assets		$71.9								$66.7

	2019								2018
	Fair		Level		Level		Level		Fair		Level		Level		Level
WPL	Value		1		2		3		Value		1		2		3
Cash and equivalents		$0.4		$0.4		$—		$—		$0.1		$0.1		$—		$—
Fixed income securities	16.7		16.7		—		—		16.6		16.6		—		—
Total OPEB plan assets		$17.1		$17.1		$—		$—		$16.7		$16.7		$—		$—

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 OPEB plan assets were as follows (in millions):

	2019								2018
	Fair		Level		Level		Level		Fair		Level		Level		Level
Alliant Energy	Value		1		2		3		Value		1		2		3
Cash and equivalents		$3.4		$3.0		$0.4		$—		$1.4		$1.1		$0.3		$—
Equity securities - U.S.	3.7		3.7		—		—		3.9		3.9		—		—
Equity securities - international	2.8		2.8		—		—		2.9		2.9		—		—
Global asset securities	0.5		0.5		—		—		0.4		0.4		—		—
Fixed income securities	68.5		67.8		0.7		—		68.2		67.5		0.7		—
Total assets in fair value hierarchy	78.9			$77.8		$1.1		$—	76.8			$75.8		$1.0		$—
Assets measured at net asset value	26.0								22.3
Total OPEB plan assets		$104.9								$99.1

	2019								2018
	Fair		Level		Level		Level		Fair		Level		Level		Level
IPL	Value		1		2		3		Value		1		2		3
Cash and equivalents		$1.5		$1.5		$—		$—		$0.7		$0.7		$—		$—
Fixed income securities	48.3		48.3		—		—		47.0		47.0		—		—
Total assets in fair value hierarchy	49.8			$49.8		$—		$—	47.7			$47.7		$—		$—
Assets measured at net asset value	22.1								19.0
Total OPEB plan assets		$71.9								$66.7

	2019								2018
	Fair		Level		Level		Level		Fair		Level		Level		Level
WPL	Value		1		2		3		Value		1		2		3
Cash and equivalents		$0.4		$0.4		$—		$—		$0.1		$0.1		$—		$—
Fixed income securities	16.7		16.7		—		—		16.6		16.6		—		—
Total OPEB plan assets		$17.1		$17.1		$—		$—		$16.7		$16.7		$—		$—

At December 31, 2019, 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%	3%
Equity securities - U.S.	0	%	-	46%	25%
Equity securities - international	0	%	-	34%	2%
Fixed income securities	20	%	-	100%	70%

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, 2019, 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%	3%
Equity securities - U.S.	0	%	-	46%	25%
Equity securities - international	0	%	-	34%	2%
Fixed income securities	20	%	-	100%	70%

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

	2019								2018
	Fair		Level		Level		Level		Fair		Level		Level		Level
Alliant Energy	Value		1		2		3		Value		1		2		3
Cash and equivalents		$3.4		$3.0		$0.4		$—		$1.4		$1.1		$0.3		$—
Equity securities - U.S.	3.7		3.7		—		—		3.9		3.9		—		—
Equity securities - international	2.8		2.8		—		—		2.9		2.9		—		—
Global asset securities	0.5		0.5		—		—		0.4		0.4		—		—
Fixed income securities	68.5		67.8		0.7		—		68.2		67.5		0.7		—
Total assets in fair value hierarchy	78.9			$77.8		$1.1		$—	76.8			$75.8		$1.0		$—
Assets measured at net asset value	26.0								22.3
Total OPEB plan assets		$104.9								$99.1

	2019								2018
	Fair		Level		Level		Level		Fair		Level		Level		Level
IPL	Value		1		2		3		Value		1		2		3
Cash and equivalents		$1.5		$1.5		$—		$—		$0.7		$0.7		$—		$—
Fixed income securities	48.3		48.3		—		—		47.0		47.0		—		—
Total assets in fair value hierarchy	49.8			$49.8		$—		$—	47.7			$47.7		$—		$—
Assets measured at net asset value	22.1								19.0
Total OPEB plan assets		$71.9								$66.7

	2019								2018
	Fair		Level		Level		Level		Fair		Level		Level		Level
WPL	Value		1		2		3		Value		1		2		3
Cash and equivalents		$0.4		$0.4		$—		$—		$0.1		$0.1		$—		$—
Fixed income securities	16.7		16.7		—		—		16.6		16.6		—		—
Total OPEB plan assets		$17.1		$17.1		$—		$—		$16.7		$16.7		$—		$—

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
	2019		2018		2017		2019		2018		2017		2019		2018		2017
401(k) costs		$25.5		$25.1		$24.8		$13.0		$13.0		$12.8		$11.5		$11.2		$11.1

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
	2019		2018		2017		2019		2018		2017		2019		2018		2017
401(k) costs		$25.5		$25.1		$24.8		$13.0		$13.0		$12.8		$11.5		$11.2		$11.1

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
	2019		2018		2017		2019		2018		2017		2019		2018		2017
401(k) costs		$25.5		$25.1		$24.8		$13.0		$13.0		$12.8		$11.5		$11.2		$11.1

Performance Shares and Performance Units Liability Awards [Member]

Defined Benefit Plan Disclosure [Line Items]

Schedule Of Equity-based Compensation Plans Activity

Additional information related to the fair value of nonvested performance shares and performance units at December 31, 2019, by year of grant, was as follows:

	Performance Shares (granted prior to 2019)						Performance Units (granted prior to 2019)
	2018 Grant			2017 Grant			2018 Grant			2017 Grant
Nonvested awards at target	68,307			63,565			17,622			16,952
Estimated payout percentage based on performance criteria	118		%	155		%	118		%	155		%
Fair values of each nonvested award		$64.57			$84.82			$64.57			$84.82

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

	Performance Shares (granted prior to 2019)						Performance Units (granted prior to 2019)
	2019		2018		2017		2019		2018		2017
Nonvested awards, January 1	203,188		223,511		257,599		57,761		71,737		93,320
Granted	—		74,163		65,350		—		19,840		21,558
Vested	(66,322	)	(90,806	)	(99,438	)	(20,131	)	(31,910	)	(37,395	)
Forfeited	(4,994	)	(3,680	)	—		(3,056	)	(1,906	)	(5,746	)
Nonvested awards, December 31	131,872		203,188		223,511		34,574		57,761		71,737

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 (granted prior to 2019)			Performance Units (granted prior to 2019)
	2019	2018	2017	2019	2018	2017
	2016 Grant	2015 Grant	2014 Grant	2016 Grant	2015 Grant	2014 Grant
Performance awards vested	66,322	90,806	99,438	20,131	31,910	37,395
Percentage of target number of performance awards	142.5%	137.5%	147.5%	142.5%	137.5%	147.5%
Aggregate payout value (in millions)	$4.3	$5.3	$5.6	$1.3	$1.4	$1.5
Payout - cash (in millions)	$3.7	$4.9	$5.1	$1.3	$1.4	$1.5
Payout - common stock shares issued	6,447	5,078	5,185	N/A	N/A	N/A

Performance Shares Equity Awards [Member]

Defined Benefit Plan Disclosure [Line Items]

Schedule Of Equity-based Compensation Plans Activity

A summary of the 2019 performance shares activity, with amounts representing the target number of awards, was as follows:

	2019
	Performance Shares - Equity		Weighted Average Grant Date Fair Value
Nonvested awards, January 1	—			$—
Granted	91,816		47.23
Forfeited	(17,623	)	46.35
Nonvested awards, December 31	74,193		47.44

Performance Restricted Stock Units Equity Awards [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:

	2019				2018				2017
	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	203,188			$37.23	132,705			$36.50	67,355		$33.96
Granted	91,816		46.10		74,163		38.60		65,350	39.12
Vested	(66,322	)	33.93		—		—		—	—
Forfeited	(22,617	)	44.00		(3,680	)	38.60		—	—
Nonvested units, December 31	206,065		41.50		203,188		37.23		132,705	36.50

Restricted Stock Units Equity Awards [Member]

Defined Benefit Plan Disclosure [Line Items]

Schedule Of Equity-based Compensation Plans Activity

A summary of the 2019 restricted stock units activity was as follows:

	2019
	Restricted Stock Units - Equity		Weighted Average Grant Date Fair Value
Nonvested units, January 1	—			$—
Granted	105,348		45.98
Forfeited	(16,067	)	45.63
Nonvested units, December 31	89,281		46.04

Restricted Stock Unit Liability Awards [Member]

Defined Benefit Plan Disclosure [Line Items]

Schedule Of Equity-based Compensation Plans Activity

A summary of the restricted stock units granted prior to 2019 activity was as follows:

	2019		2018		2017
Nonvested units, January 1	174,163		113,749		57,736
Granted	—		63,568		56,013
Vested	(56,849	)	—		—
Forfeited	(4,281	)	(3,154	)	—
Nonvested units, December 31	113,033		174,163		113,749