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Debt (Tables)
 12 Months Ended
Dec. 31, 2021
Debt Instrument [Line Items]  
Schedule of Other Short-term Borrowings Information regarding Alliant Energy’s, IPL’s and WPL’s commercial paper, and Alliant Energy’s and WPL’s borrowings under the single credit facility, classified as short-term debt was as follows (dollars in millions):
Alliant EnergyIPLWPL
December 31202120202021202020212020
Amount outstanding$515$389$—$—$236$257
Weighted average interest rates0.2%0.2%N/AN/A0.2%0.1%
Available credit facility capacity$485$611$250$250$64$43
Alliant EnergyIPLWPL
For the year ended202120202021202020212020
Maximum amount outstanding (based on daily outstanding balances)$648$495$19$8$320$266
Average amount outstanding (based on daily outstanding balances)$459$292$—$—$172$117
Weighted average interest rates0.2%0.7%0.2%0.5%0.1%0.7%
Schedule of Long-term Debt Long-term debt, net as of December 31 was as follows (dollars in millions):
20212020
Alliant EnergyIPLWPLAlliant EnergyIPLWPL
Senior Debentures (a):
3.25%, due 2024
$500 $500 $— $500 $500 $— 
3.4%, due 2025
250 250 — 250 250 — 
5.5%, due 2025
50 50 — 50 50 — 
4.1%, due 2028
500 500 — 500 500 — 
3.6%, due 2029
300 300 — 300 300 — 
2.3%, due 2030
400 400 — 400 400 — 
6.45%, due 2033
100 100 — 100 100 — 
6.3%, due 2034
125 125 — 125 125 — 
6.25%, due 2039
300 300 — 300 300 — 
4.7%, due 2043
250 250 — 250 250 — 
3.7%, due 2046
300 300 — 300 300 — 
3.5%, due 2049
300 300 — 300 300 — 
3.1%, due 2051 (b)
300 300 — — — — 
3,675 3,675 — 3,375 3,375 — 
Debentures (a):
2.25%, due 2022
250 — 250 250 — 250 
3.05%, due 2027
300 — 300 300 — 300 
3%, due 2029
350 — 350 350 — 350 
1.95%, due 2031 (c)
300 — 300 — — — 
6.25%, due 2034
100 — 100 100 — 100 
6.375%, due 2037
300 — 300 300 — 300 
7.6%, due 2038
250 — 250 250 — 250 
4.1%, due 2044
250 — 250 250 — 250 
3.65%, due 2050
350 — 350 350 — 350 
2,450 — 2,450 2,150 — 2,150 
Other:
AEF term loan credit agreement through March 2022, 1% at December 31, 2021 (with Alliant Energy as guarantor)
300 — — 300 — — 
Corporate Services 3.45% senior notes, due 2022 (a)
75 — — 75 — — 
AEF 3.75% senior notes, due 2023 (with Alliant Energy as guarantor) (a)
400 — — 400 — — 
AEF 1.4% senior notes, due 2026 (with Alliant Energy as guarantor) (a)
200 — — 200 — — 
AEF 4.25% senior notes, due 2028 (with Alliant Energy as guarantor) (a)
300 — — 300 — — 
Sheboygan Power, LLC 5.06% senior secured notes, due 2022 to 2024 (secured by the Sheboygan Falls Energy Facility and related assets) (a)
24 — — 31 — — 
Other, 1% at December 31, 2021, due 2022 to 2025
1 — — 2 — — 
1,300 — — 1,308 — — 
Subtotal7,425 3,675 2,450 6,833 3,375 2,150 
Current maturities(633)— (250)(8)— — 
Unamortized debt issuance costs(42)(23)(15)(41)(22)(14)
Unamortized debt (discount) and premium, net(15)(9)(6)(15)(8)(6)
Long-term debt, net (d)$6,735 $3,643 $2,179 $6,769 $3,345 $2,130 

(a)Contains optional redemption provisions which, if elected by the issuer at its sole discretion, could require material redemption premium payments by the issuer. The redemption premium payments under these optional redemption provisions are variable and dependent on applicable U.S. Treasury rates at the time of redemption.
(b)In November 2021, IPL issued $300 million of 3.1% senior debentures due 2051. The net proceeds from the issuance were used by IPL to retire its cumulative preferred stock in 2021 and for general corporate purposes.
(c)In September 2021, WPL issued $300 million of 1.95% debentures due 2031. The debentures were issued as green bonds, and an amount in excess of the net proceeds was disbursed for the construction and development of WPL’s wind and solar EGUs.
(d)There were no significant sinking fund requirements related to the outstanding long-term debt.
Schedule of Maturities of Long-term Debt At December 31, 2021, long-term debt maturities for 2022 through 2026 were as follows (in millions):
20222023202420252026
IPL$—$—$500$300$—
WPL250————
Corporate Services75————
AEF3084089—200
Alliant Energy$633$408$509$300$200
IPL [Member]  
Debt Instrument [Line Items]  
Schedule of Other Short-term Borrowings Information regarding Alliant Energy’s, IPL’s and WPL’s commercial paper, and Alliant Energy’s and WPL’s borrowings under the single credit facility, classified as short-term debt was as follows (dollars in millions):
Alliant EnergyIPLWPL
December 31202120202021202020212020
Amount outstanding$515$389$—$—$236$257
Weighted average interest rates0.2%0.2%N/AN/A0.2%0.1%
Available credit facility capacity$485$611$250$250$64$43
Alliant EnergyIPLWPL
For the year ended202120202021202020212020
Maximum amount outstanding (based on daily outstanding balances)$648$495$19$8$320$266
Average amount outstanding (based on daily outstanding balances)$459$292$—$—$172$117
Weighted average interest rates0.2%0.7%0.2%0.5%0.1%0.7%
Schedule of Long-term Debt Long-term debt, net as of December 31 was as follows (dollars in millions):
20212020
Alliant EnergyIPLWPLAlliant EnergyIPLWPL
Senior Debentures (a):
3.25%, due 2024
$500 $500 $— $500 $500 $— 
3.4%, due 2025
250 250 — 250 250 — 
5.5%, due 2025
50 50 — 50 50 — 
4.1%, due 2028
500 500 — 500 500 — 
3.6%, due 2029
300 300 — 300 300 — 
2.3%, due 2030
400 400 — 400 400 — 
6.45%, due 2033
100 100 — 100 100 — 
6.3%, due 2034
125 125 — 125 125 — 
6.25%, due 2039
300 300 — 300 300 — 
4.7%, due 2043
250 250 — 250 250 — 
3.7%, due 2046
300 300 — 300 300 — 
3.5%, due 2049
300 300 — 300 300 — 
3.1%, due 2051 (b)
300 300 — — — — 
3,675 3,675 — 3,375 3,375 — 
Debentures (a):
2.25%, due 2022
250 — 250 250 — 250 
3.05%, due 2027
300 — 300 300 — 300 
3%, due 2029
350 — 350 350 — 350 
1.95%, due 2031 (c)
300 — 300 — — — 
6.25%, due 2034
100 — 100 100 — 100 
6.375%, due 2037
300 — 300 300 — 300 
7.6%, due 2038
250 — 250 250 — 250 
4.1%, due 2044
250 — 250 250 — 250 
3.65%, due 2050
350 — 350 350 — 350 
2,450 — 2,450 2,150 — 2,150 
Other:
AEF term loan credit agreement through March 2022, 1% at December 31, 2021 (with Alliant Energy as guarantor)
300 — — 300 — — 
Corporate Services 3.45% senior notes, due 2022 (a)
75 — — 75 — — 
AEF 3.75% senior notes, due 2023 (with Alliant Energy as guarantor) (a)
400 — — 400 — — 
AEF 1.4% senior notes, due 2026 (with Alliant Energy as guarantor) (a)
200 — — 200 — — 
AEF 4.25% senior notes, due 2028 (with Alliant Energy as guarantor) (a)
300 — — 300 — — 
Sheboygan Power, LLC 5.06% senior secured notes, due 2022 to 2024 (secured by the Sheboygan Falls Energy Facility and related assets) (a)
24 — — 31 — — 
Other, 1% at December 31, 2021, due 2022 to 2025
1 — — 2 — — 
1,300 — — 1,308 — — 
Subtotal7,425 3,675 2,450 6,833 3,375 2,150 
Current maturities(633)— (250)(8)— — 
Unamortized debt issuance costs(42)(23)(15)(41)(22)(14)
Unamortized debt (discount) and premium, net(15)(9)(6)(15)(8)(6)
Long-term debt, net (d)$6,735 $3,643 $2,179 $6,769 $3,345 $2,130 

(a)Contains optional redemption provisions which, if elected by the issuer at its sole discretion, could require material redemption premium payments by the issuer. The redemption premium payments under these optional redemption provisions are variable and dependent on applicable U.S. Treasury rates at the time of redemption.
(b)In November 2021, IPL issued $300 million of 3.1% senior debentures due 2051. The net proceeds from the issuance were used by IPL to retire its cumulative preferred stock in 2021 and for general corporate purposes.
(c)In September 2021, WPL issued $300 million of 1.95% debentures due 2031. The debentures were issued as green bonds, and an amount in excess of the net proceeds was disbursed for the construction and development of WPL’s wind and solar EGUs.
(d)There were no significant sinking fund requirements related to the outstanding long-term debt.
Schedule of Maturities of Long-term Debt At December 31, 2021, long-term debt maturities for 2022 through 2026 were as follows (in millions):
20222023202420252026
IPL$—$—$500$300$—
WPL250————
Corporate Services75————
AEF3084089—200
Alliant Energy$633$408$509$300$200
WPL [Member]  
Debt Instrument [Line Items]  
Schedule of Other Short-term Borrowings Information regarding Alliant Energy’s, IPL’s and WPL’s commercial paper, and Alliant Energy’s and WPL’s borrowings under the single credit facility, classified as short-term debt was as follows (dollars in millions):
Alliant EnergyIPLWPL
December 31202120202021202020212020
Amount outstanding$515$389$—$—$236$257
Weighted average interest rates0.2%0.2%N/AN/A0.2%0.1%
Available credit facility capacity$485$611$250$250$64$43
Alliant EnergyIPLWPL
For the year ended202120202021202020212020
Maximum amount outstanding (based on daily outstanding balances)$648$495$19$8$320$266
Average amount outstanding (based on daily outstanding balances)$459$292$—$—$172$117
Weighted average interest rates0.2%0.7%0.2%0.5%0.1%0.7%
Schedule of Long-term Debt Long-term debt, net as of December 31 was as follows (dollars in millions):
20212020
Alliant EnergyIPLWPLAlliant EnergyIPLWPL
Senior Debentures (a):
3.25%, due 2024
$500 $500 $— $500 $500 $— 
3.4%, due 2025
250 250 — 250 250 — 
5.5%, due 2025
50 50 — 50 50 — 
4.1%, due 2028
500 500 — 500 500 — 
3.6%, due 2029
300 300 — 300 300 — 
2.3%, due 2030
400 400 — 400 400 — 
6.45%, due 2033
100 100 — 100 100 — 
6.3%, due 2034
125 125 — 125 125 — 
6.25%, due 2039
300 300 — 300 300 — 
4.7%, due 2043
250 250 — 250 250 — 
3.7%, due 2046
300 300 — 300 300 — 
3.5%, due 2049
300 300 — 300 300 — 
3.1%, due 2051 (b)
300 300 — — — — 
3,675 3,675 — 3,375 3,375 — 
Debentures (a):
2.25%, due 2022
250 — 250 250 — 250 
3.05%, due 2027
300 — 300 300 — 300 
3%, due 2029
350 — 350 350 — 350 
1.95%, due 2031 (c)
300 — 300 — — — 
6.25%, due 2034
100 — 100 100 — 100 
6.375%, due 2037
300 — 300 300 — 300 
7.6%, due 2038
250 — 250 250 — 250 
4.1%, due 2044
250 — 250 250 — 250 
3.65%, due 2050
350 — 350 350 — 350 
2,450 — 2,450 2,150 — 2,150 
Other:
AEF term loan credit agreement through March 2022, 1% at December 31, 2021 (with Alliant Energy as guarantor)
300 — — 300 — — 
Corporate Services 3.45% senior notes, due 2022 (a)
75 — — 75 — — 
AEF 3.75% senior notes, due 2023 (with Alliant Energy as guarantor) (a)
400 — — 400 — — 
AEF 1.4% senior notes, due 2026 (with Alliant Energy as guarantor) (a)
200 — — 200 — — 
AEF 4.25% senior notes, due 2028 (with Alliant Energy as guarantor) (a)
300 — — 300 — — 
Sheboygan Power, LLC 5.06% senior secured notes, due 2022 to 2024 (secured by the Sheboygan Falls Energy Facility and related assets) (a)
24 — — 31 — — 
Other, 1% at December 31, 2021, due 2022 to 2025
1 — — 2 — — 
1,300 — — 1,308 — — 
Subtotal7,425 3,675 2,450 6,833 3,375 2,150 
Current maturities(633)— (250)(8)— — 
Unamortized debt issuance costs(42)(23)(15)(41)(22)(14)
Unamortized debt (discount) and premium, net(15)(9)(6)(15)(8)(6)
Long-term debt, net (d)$6,735 $3,643 $2,179 $6,769 $3,345 $2,130 

(a)Contains optional redemption provisions which, if elected by the issuer at its sole discretion, could require material redemption premium payments by the issuer. The redemption premium payments under these optional redemption provisions are variable and dependent on applicable U.S. Treasury rates at the time of redemption.
(b)In November 2021, IPL issued $300 million of 3.1% senior debentures due 2051. The net proceeds from the issuance were used by IPL to retire its cumulative preferred stock in 2021 and for general corporate purposes.
(c)In September 2021, WPL issued $300 million of 1.95% debentures due 2031. The debentures were issued as green bonds, and an amount in excess of the net proceeds was disbursed for the construction and development of WPL’s wind and solar EGUs.
(d)There were no significant sinking fund requirements related to the outstanding long-term debt.
Schedule of Maturities of Long-term Debt At December 31, 2021, long-term debt maturities for 2022 through 2026 were as follows (in millions):
20222023202420252026
IPL$—$—$500$300$—
WPL250————
Corporate Services75————
AEF3084089—200
Alliant Energy$633$408$509$300$200