Fair Value Measurements (Tables)

3 Months Ended

Mar. 31, 2021

Statement [Line Items]

Fair Value Measurements

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

Alliant Energy	March 31, 2021					December 31, 2020
		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	$8	$8	$—	$—	$8	$44	$44	$—	$—	$44
Derivatives	28	—	12	16	28	34	—	5	29	34
Deferred proceeds	107	—	—	107	107	188	—	—	188	188
Liabilities:
Derivatives	13	—	13	—	13	25	—	25	—	25
Long-term debt (incl. current maturities)	6,779	—	7,613	1	7,614	6,777	—	8,107	2	8,109

IPL	March 31, 2021					December 31, 2020
		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	$8	$8	$—	$—	$8	$44	$44	$—	$—	$44
Derivatives	19	—	4	15	19	29	—	3	26	29
Deferred proceeds	107	—	—	107	107	188	—	—	188	188
Liabilities:
Derivatives	6	—	6	—	6	12	—	12	—	12
Long-term debt	3,346	—	3,745	—	3,745	3,345	—	4,021	—	4,021

WPL	March 31, 2021					December 31, 2020
		Fair Value					Fair Value
	Carrying	Level	Level	Level		Carrying	Level	Level	Level
	Amount	1	2	3	Total	Amount	1	2	3	Total
Assets:
Derivatives	$9	$—	$8	$1	$9	$5	$—	$2	$3	$5
Liabilities:
Derivatives	7	—	7	—	7	13	—	13	—	13
Long-term debt	2,131	—	2,495	—	2,495	2,130	—	2,690	—	2,690

Fair Value Measurements Using Significant Unobservable Inputs

Information for Alliant Energy’s and IPL’s fair value measurements using significant unobservable inputs (Level 3 inputs) was as follows (in millions). Such amounts for WPL were not material.

Alliant Energy	Commodity Contract Derivative
	Assets and (Liabilities), net		Deferred Proceeds
Three Months Ended March 31	2021	2020	2021	2020
Beginning balance, January 1	$29	$21	$188	$188
Total net losses included in changes in net assets (realized/unrealized)	(6)	(3)	—	—
Settlements (a)	(7)	(4)	(81)	—
Ending balance, March 31	$16	$14	$107	$188
The amount of total net losses for the period included in changes in net assets attributable to the change in unrealized losses relating to assets and liabilities held at March 31	($6)	($3)	$—	$—

IPL	Commodity Contract Derivative
	Assets and (Liabilities), net		Deferred Proceeds
Three Months Ended March 31	2021	2020	2021	2020
Beginning balance, January 1	$26	$18	$188	$188
Total net losses included in changes in net assets (realized/unrealized)	(5)	(2)	—	—
Settlements (a)	(6)	(3)	(81)	—
Ending balance, March 31	$15	$13	$107	$188
The amount of total net losses for the period included in changes in net assets attributable to the change in unrealized losses relating to assets and liabilities held at March 31	($6)	($2)	$—	$—

(a)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

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

	Alliant Energy		IPL		WPL
	Excluding FTRs	FTRs	Excluding FTRs	FTRs	Excluding FTRs	FTRs
March 31, 2021	$11	$5	$11	$4	$—	$1
December 31, 2020	18	11	17	9	1	2

IPL [Member]

Statement [Line Items]

Fair Value Measurements

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

Alliant Energy	March 31, 2021					December 31, 2020
		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	$8	$8	$—	$—	$8	$44	$44	$—	$—	$44
Derivatives	28	—	12	16	28	34	—	5	29	34
Deferred proceeds	107	—	—	107	107	188	—	—	188	188
Liabilities:
Derivatives	13	—	13	—	13	25	—	25	—	25
Long-term debt (incl. current maturities)	6,779	—	7,613	1	7,614	6,777	—	8,107	2	8,109

IPL	March 31, 2021					December 31, 2020
		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	$8	$8	$—	$—	$8	$44	$44	$—	$—	$44
Derivatives	19	—	4	15	19	29	—	3	26	29
Deferred proceeds	107	—	—	107	107	188	—	—	188	188
Liabilities:
Derivatives	6	—	6	—	6	12	—	12	—	12
Long-term debt	3,346	—	3,745	—	3,745	3,345	—	4,021	—	4,021

WPL	March 31, 2021					December 31, 2020
		Fair Value					Fair Value
	Carrying	Level	Level	Level		Carrying	Level	Level	Level
	Amount	1	2	3	Total	Amount	1	2	3	Total
Assets:
Derivatives	$9	$—	$8	$1	$9	$5	$—	$2	$3	$5
Liabilities:
Derivatives	7	—	7	—	7	13	—	13	—	13
Long-term debt	2,131	—	2,495	—	2,495	2,130	—	2,690	—	2,690

Fair Value Measurements Using Significant Unobservable Inputs

Information for Alliant Energy’s and IPL’s fair value measurements using significant unobservable inputs (Level 3 inputs) was as follows (in millions). Such amounts for WPL were not material.

Alliant Energy	Commodity Contract Derivative
	Assets and (Liabilities), net		Deferred Proceeds
Three Months Ended March 31	2021	2020	2021	2020
Beginning balance, January 1	$29	$21	$188	$188
Total net losses included in changes in net assets (realized/unrealized)	(6)	(3)	—	—
Settlements (a)	(7)	(4)	(81)	—
Ending balance, March 31	$16	$14	$107	$188
The amount of total net losses for the period included in changes in net assets attributable to the change in unrealized losses relating to assets and liabilities held at March 31	($6)	($3)	$—	$—

IPL	Commodity Contract Derivative
	Assets and (Liabilities), net		Deferred Proceeds
Three Months Ended March 31	2021	2020	2021	2020
Beginning balance, January 1	$26	$18	$188	$188
Total net losses included in changes in net assets (realized/unrealized)	(5)	(2)	—	—
Settlements (a)	(6)	(3)	(81)	—
Ending balance, March 31	$15	$13	$107	$188
The amount of total net losses for the period included in changes in net assets attributable to the change in unrealized losses relating to assets and liabilities held at March 31	($6)	($2)	$—	$—

(a)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

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

	Alliant Energy		IPL		WPL
	Excluding FTRs	FTRs	Excluding FTRs	FTRs	Excluding FTRs	FTRs
March 31, 2021	$11	$5	$11	$4	$—	$1
December 31, 2020	18	11	17	9	1	2

WPL [Member]

Statement [Line Items]

Fair Value Measurements

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

Alliant Energy	March 31, 2021					December 31, 2020
		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	$8	$8	$—	$—	$8	$44	$44	$—	$—	$44
Derivatives	28	—	12	16	28	34	—	5	29	34
Deferred proceeds	107	—	—	107	107	188	—	—	188	188
Liabilities:
Derivatives	13	—	13	—	13	25	—	25	—	25
Long-term debt (incl. current maturities)	6,779	—	7,613	1	7,614	6,777	—	8,107	2	8,109

IPL	March 31, 2021					December 31, 2020
		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	$8	$8	$—	$—	$8	$44	$44	$—	$—	$44
Derivatives	19	—	4	15	19	29	—	3	26	29
Deferred proceeds	107	—	—	107	107	188	—	—	188	188
Liabilities:
Derivatives	6	—	6	—	6	12	—	12	—	12
Long-term debt	3,346	—	3,745	—	3,745	3,345	—	4,021	—	4,021

WPL	March 31, 2021					December 31, 2020
		Fair Value					Fair Value
	Carrying	Level	Level	Level		Carrying	Level	Level	Level
	Amount	1	2	3	Total	Amount	1	2	3	Total
Assets:
Derivatives	$9	$—	$8	$1	$9	$5	$—	$2	$3	$5
Liabilities:
Derivatives	7	—	7	—	7	13	—	13	—	13
Long-term debt	2,131	—	2,495	—	2,495	2,130	—	2,690	—	2,690

Fair Value Of Net Derivative Assets

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

	Alliant Energy		IPL		WPL
	Excluding FTRs	FTRs	Excluding FTRs	FTRs	Excluding FTRs	FTRs
March 31, 2021	$11	$5	$11	$4	$—	$1
December 31, 2020	18	11	17	9	1	2