Fair Value Measurements (Tables)

12 Months Ended

Dec. 31, 2020

Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]

Recurring Fair Value Measurements

Carrying amounts and the related estimated fair values of other financial instruments at December 31 were as follows (in millions):

Alliant Energy	2020					2019
		Fair Value					Fair Value
	Carrying	Level	Level	Level		Carrying	Level	Level	Level
	Amount	1	2	3	Total	Amount	1	2	3	Total
Assets:
Money market fund investments	$44	$44	$—	$—	$44	$5	$5	$—	$—	$5
Derivatives	34	—	5	29	34	27	—	5	22	27
Deferred proceeds	188	—	—	188	188	188	—	—	188	188
Liabilities and equity:
Derivatives	25	—	25	—	25	38	—	37	1	38
Long-term debt (incl. current maturities)	6,777	—	8,107	2	8,109	6,190	—	6,918	2	6,920

IPL	2020					2019
		Fair Value					Fair Value
	Carrying	Level	Level	Level		Carrying	Level	Level	Level
	Amount	1	2	3	Total	Amount	1	2	3	Total
Assets:
Money market fund investments	$44	$44	$—	$—	$44	$5	$5	$—	$—	$5
Derivatives	29	—	3	26	29	22	—	3	19	22
Deferred proceeds	188	—	—	188	188	188	—	—	188	188
Liabilities and equity:
Derivatives	12	—	12	—	12	18	—	17	1	18
Long-term debt (incl. current maturities)	3,345	—	4,021	—	4,021	3,147	—	3,489	—	3,489

WPL	2020					2019
		Fair Value					Fair Value
	Carrying	Level	Level	Level		Carrying	Level	Level	Level
	Amount	1	2	3	Total	Amount	1	2	3	Total
Assets:
Derivatives	$5	$—	$2	$3	$5	$5	$—	$2	$3	$5
Liabilities and equity:
Derivatives	13	—	13	—	13	20	—	20	—	20
Long-term debt (incl. current maturities)	2,130	—	2,690	—	2,690	1,933	—	2,268	—	2,268

Fair Value Measurements Using Significant Unobservable Inputs

Information for fair value measurements using significant unobservable inputs (Level 3 inputs) was as follows (in millions):

Alliant Energy	Commodity Contract Derivative
	Assets and (Liabilities), net		Deferred Proceeds
	2020	2019	2020	2019
Beginning balance, January 1	$21	$12	$188	$119
Total net gains included in changes in net assets (realized/unrealized)	11	8	—	—
Transfers out of Level 3 (a)	—	4	—	—
Purchases	14	14	—	—
Sales	(1)	—	—	—
Settlements (b)	(16)	(17)	—	69
Ending balance, December 31	$29	$21	$188	$188
The amount of total net gains for the period included in changes in net assets attributable to the change in unrealized gains relating to assets and liabilities held at December 31	$11	$11	$—	$—

IPL	Commodity Contract Derivative
	Assets and (Liabilities), net		Deferred Proceeds
	2020	2019	2020	2019
Beginning balance, January 1	$18	$9	$188	$119
Total net gains included in changes in net assets (realized/unrealized)	10	11	—	—
Transfers out of Level 3 (a)	—	2	—	—
Purchases	11	9	—	—
Sales	(1)	—	—	—
Settlements (b)	(12)	(13)	—	69
Ending balance, December 31	$26	$18	$188	$188
The amount of total net gains for the period included in changes in net assets attributable to the change in unrealized gains relating to assets and liabilities held at December 31	$10	$12	$—	$—

(a)Observable market inputs became available for certain commodity contracts previously classified as Level 3 for transfers out of Level 3.

(b)Settlements related to deferred proceeds are due to the change in the carrying amount of receivables sold less the allowance for expected credit losses associated with the receivables sold and cash amounts received from the receivables sold.

Fair Value Of Net Derivative Assets (Liabilities)

The fair value of FTR and natural gas commodity contracts categorized as Level 3 was recognized as net derivative assets at December 31 as follows (in millions):

	Alliant Energy		IPL		WPL
	Excluding FTRs	FTRs	Excluding FTRs	FTRs	Excluding FTRs	FTRs
2020	$18	$11	$17	$9	$1	$2
2019	15	7	14	5	1	2

IPL [Member]

Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]

Recurring Fair Value Measurements

Carrying amounts and the related estimated fair values of other financial instruments at December 31 were as follows (in millions):

Alliant Energy	2020					2019
		Fair Value					Fair Value
	Carrying	Level	Level	Level		Carrying	Level	Level	Level
	Amount	1	2	3	Total	Amount	1	2	3	Total
Assets:
Money market fund investments	$44	$44	$—	$—	$44	$5	$5	$—	$—	$5
Derivatives	34	—	5	29	34	27	—	5	22	27
Deferred proceeds	188	—	—	188	188	188	—	—	188	188
Liabilities and equity:
Derivatives	25	—	25	—	25	38	—	37	1	38
Long-term debt (incl. current maturities)	6,777	—	8,107	2	8,109	6,190	—	6,918	2	6,920

IPL	2020					2019
		Fair Value					Fair Value
	Carrying	Level	Level	Level		Carrying	Level	Level	Level
	Amount	1	2	3	Total	Amount	1	2	3	Total
Assets:
Money market fund investments	$44	$44	$—	$—	$44	$5	$5	$—	$—	$5
Derivatives	29	—	3	26	29	22	—	3	19	22
Deferred proceeds	188	—	—	188	188	188	—	—	188	188
Liabilities and equity:
Derivatives	12	—	12	—	12	18	—	17	1	18
Long-term debt (incl. current maturities)	3,345	—	4,021	—	4,021	3,147	—	3,489	—	3,489

WPL	2020					2019
		Fair Value					Fair Value
	Carrying	Level	Level	Level		Carrying	Level	Level	Level
	Amount	1	2	3	Total	Amount	1	2	3	Total
Assets:
Derivatives	$5	$—	$2	$3	$5	$5	$—	$2	$3	$5
Liabilities and equity:
Derivatives	13	—	13	—	13	20	—	20	—	20
Long-term debt (incl. current maturities)	2,130	—	2,690	—	2,690	1,933	—	2,268	—	2,268

Fair Value Measurements Using Significant Unobservable Inputs

Information for fair value measurements using significant unobservable inputs (Level 3 inputs) was as follows (in millions):

Alliant Energy	Commodity Contract Derivative
	Assets and (Liabilities), net		Deferred Proceeds
	2020	2019	2020	2019
Beginning balance, January 1	$21	$12	$188	$119
Total net gains included in changes in net assets (realized/unrealized)	11	8	—	—
Transfers out of Level 3 (a)	—	4	—	—
Purchases	14	14	—	—
Sales	(1)	—	—	—
Settlements (b)	(16)	(17)	—	69
Ending balance, December 31	$29	$21	$188	$188
The amount of total net gains for the period included in changes in net assets attributable to the change in unrealized gains relating to assets and liabilities held at December 31	$11	$11	$—	$—

IPL	Commodity Contract Derivative
	Assets and (Liabilities), net		Deferred Proceeds
	2020	2019	2020	2019
Beginning balance, January 1	$18	$9	$188	$119
Total net gains included in changes in net assets (realized/unrealized)	10	11	—	—
Transfers out of Level 3 (a)	—	2	—	—
Purchases	11	9	—	—
Sales	(1)	—	—	—
Settlements (b)	(12)	(13)	—	69
Ending balance, December 31	$26	$18	$188	$188
The amount of total net gains for the period included in changes in net assets attributable to the change in unrealized gains relating to assets and liabilities held at December 31	$10	$12	$—	$—

(a)Observable market inputs became available for certain commodity contracts previously classified as Level 3 for transfers out of Level 3.

(b)Settlements related to deferred proceeds are due to the change in the carrying amount of receivables sold less the allowance for expected credit losses associated with the receivables sold and cash amounts received from the receivables sold.

Fair Value Of Net Derivative Assets (Liabilities)

The fair value of FTR and natural gas commodity contracts categorized as Level 3 was recognized as net derivative assets at December 31 as follows (in millions):

	Alliant Energy		IPL		WPL
	Excluding FTRs	FTRs	Excluding FTRs	FTRs	Excluding FTRs	FTRs
2020	$18	$11	$17	$9	$1	$2
2019	15	7	14	5	1	2

WPL [Member]

Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]

Recurring Fair Value Measurements

Carrying amounts and the related estimated fair values of other financial instruments at December 31 were as follows (in millions):

Alliant Energy	2020					2019
		Fair Value					Fair Value
	Carrying	Level	Level	Level		Carrying	Level	Level	Level
	Amount	1	2	3	Total	Amount	1	2	3	Total
Assets:
Money market fund investments	$44	$44	$—	$—	$44	$5	$5	$—	$—	$5
Derivatives	34	—	5	29	34	27	—	5	22	27
Deferred proceeds	188	—	—	188	188	188	—	—	188	188
Liabilities and equity:
Derivatives	25	—	25	—	25	38	—	37	1	38
Long-term debt (incl. current maturities)	6,777	—	8,107	2	8,109	6,190	—	6,918	2	6,920

IPL	2020					2019
		Fair Value					Fair Value
	Carrying	Level	Level	Level		Carrying	Level	Level	Level
	Amount	1	2	3	Total	Amount	1	2	3	Total
Assets:
Money market fund investments	$44	$44	$—	$—	$44	$5	$5	$—	$—	$5
Derivatives	29	—	3	26	29	22	—	3	19	22
Deferred proceeds	188	—	—	188	188	188	—	—	188	188
Liabilities and equity:
Derivatives	12	—	12	—	12	18	—	17	1	18
Long-term debt (incl. current maturities)	3,345	—	4,021	—	4,021	3,147	—	3,489	—	3,489

WPL	2020					2019
		Fair Value					Fair Value
	Carrying	Level	Level	Level		Carrying	Level	Level	Level
	Amount	1	2	3	Total	Amount	1	2	3	Total
Assets:
Derivatives	$5	$—	$2	$3	$5	$5	$—	$2	$3	$5
Liabilities and equity:
Derivatives	13	—	13	—	13	20	—	20	—	20
Long-term debt (incl. current maturities)	2,130	—	2,690	—	2,690	1,933	—	2,268	—	2,268

Fair Value Of Net Derivative Assets (Liabilities)

The fair value of FTR and natural gas commodity contracts categorized as Level 3 was recognized as net derivative assets at December 31 as follows (in millions):

	Alliant Energy		IPL		WPL
	Excluding FTRs	FTRs	Excluding FTRs	FTRs	Excluding FTRs	FTRs
2020	$18	$11	$17	$9	$1	$2
2019	15	7	14	5	1	2