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Debt (Tables)
 12 Months Ended
Dec. 31, 2022
Debt Instrument [Line Items]  
Schedule of Other Short-term Borrowings Information regarding Alliant Energy’s, IPL’s and WPL’s commercial paper classified as short-term debt was as follows (dollars in millions):
Alliant EnergyIPLWPL
December 31202220212022202120222021
Amount outstanding$642$515$—$—$290$236
Weighted average interest rates4.6%0.2%N/AN/A4.5%0.2%
Available credit facility capacity$358$485$100$250$110$64
Alliant EnergyIPLWPL
For the year ended202220212022202120222021
Maximum amount outstanding (based on daily outstanding balances)$665$648$—$19$325$320
Average amount outstanding (based on daily outstanding balances)$411$459$—$—$153$172
Weighted average interest rates2.1%0.2%—%0.2%1.6%0.1%
Schedule of Long-term Debt Long-term debt, net as of December 31 was as follows (dollars in millions):
20222021
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
300 300 — 300 300 — 
3,675 3,675 — 3,675 3,675 — 
Debentures (a):
3.05%, due 2027
300 — 300 300 — 300 
3%, due 2029
350 — 350 350 — 350 
1.95%, due 2031
300 — 300 300 — 300 
3.95%, due 2032 (b)
600 — 600 — — — 
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 
2.25% (Retired in 2022)
— — — 250 — 250 
2,800 — 2,800 2,450 — 2,450 
Other:
AEF 3.75% senior notes, due 2023 (with Alliant Energy as guarantor) (a)
400 — — 400 — — 
AEF term loan credit agreement through March 2024, 5% at December 31, 2022 (with Alliant Energy as guarantor) (c)
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 — — 
AEF 3.6% senior notes, due 2032 (with Alliant Energy as guarantor) (a)(d)
350 — — — — — 
Sheboygan Power, LLC 5.06% senior secured notes, due 2023 to 2024 (secured by the Sheboygan Falls Energy Facility and related assets) (a)
17 — — 24 — — 
AEF term loan credit agreement, 1% at December 31, 2021 (with Alliant Energy as guarantor) (Retired in 2022)
— — — 300 — — 
Corporate Services 3.45% senior notes (Retired in 2022)
— — — 75 — — 
Other, 1% at December 31, 2022, due 2023 to 2025
1 — — 1 — — 
1,668 — — 1,300 — — 
Subtotal8,143 3,675 2,800 7,425 3,675 2,450 
Current maturities(408)— — (633)— (250)
Unamortized debt issuance costs(45)(21)(19)(42)(23)(15)
Unamortized debt (discount) and premium, net(22)(8)(11)(15)(9)(6)
Long-term debt, net (e)$7,668 $3,646 $2,770 $6,735 $3,643 $2,179 

(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 August 2022, WPL issued $600 million of 3.95% debentures due 2032. The debentures were issued as green bonds, and an amount equal to or in excess of the net proceeds were disbursed for the development and acquisition of WPL’s solar EGUs.
(c)In March 2022, AEF entered into a $300 million variable rate term loan credit agreement and used the borrowings under this agreement to retire its $300 million variable rate term loan credit agreement that expired in March 2022. In December 2022, AEF increased the amount outstanding under the new term loan credit agreement by $100 million and used the additional borrowings to reduce Alliant Energy’s outstanding commercial paper and for general corporate purposes. In January 2023, AEF entered into a $300 million interest rate swap maturing in January 2026. Under the terms of the swap, AEF exchanged variable rate borrowings for a fixed rate of 3.93%.
(d)In February 2022, AEF issued $350 million of 3.6% senior notes due 2032. The net proceeds from the issuance were used to reduce Alliant Energy’s outstanding commercial paper and for general corporate purposes.
(e)There were no significant sinking fund requirements related to the outstanding long-term debt.
Schedule of Maturities of Long-term Debt At December 31, 2022, long-term debt maturities for 2023 through 2027 were as follows (in millions):
20232024202520262027
IPL$—$500$300$—$—
WPL————300
AEF408409—200—
Alliant Energy$408$909$300$200$300
IPL [Member]  
Debt Instrument [Line Items]  
Schedule of Other Short-term Borrowings Information regarding Alliant Energy’s, IPL’s and WPL’s commercial paper classified as short-term debt was as follows (dollars in millions):
Alliant EnergyIPLWPL
December 31202220212022202120222021
Amount outstanding$642$515$—$—$290$236
Weighted average interest rates4.6%0.2%N/AN/A4.5%0.2%
Available credit facility capacity$358$485$100$250$110$64
Alliant EnergyIPLWPL
For the year ended202220212022202120222021
Maximum amount outstanding (based on daily outstanding balances)$665$648$—$19$325$320
Average amount outstanding (based on daily outstanding balances)$411$459$—$—$153$172
Weighted average interest rates2.1%0.2%—%0.2%1.6%0.1%
Schedule of Long-term Debt Long-term debt, net as of December 31 was as follows (dollars in millions):
20222021
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
300 300 — 300 300 — 
3,675 3,675 — 3,675 3,675 — 
Debentures (a):
3.05%, due 2027
300 — 300 300 — 300 
3%, due 2029
350 — 350 350 — 350 
1.95%, due 2031
300 — 300 300 — 300 
3.95%, due 2032 (b)
600 — 600 — — — 
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 
2.25% (Retired in 2022)
— — — 250 — 250 
2,800 — 2,800 2,450 — 2,450 
Other:
AEF 3.75% senior notes, due 2023 (with Alliant Energy as guarantor) (a)
400 — — 400 — — 
AEF term loan credit agreement through March 2024, 5% at December 31, 2022 (with Alliant Energy as guarantor) (c)
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 — — 
AEF 3.6% senior notes, due 2032 (with Alliant Energy as guarantor) (a)(d)
350 — — — — — 
Sheboygan Power, LLC 5.06% senior secured notes, due 2023 to 2024 (secured by the Sheboygan Falls Energy Facility and related assets) (a)
17 — — 24 — — 
AEF term loan credit agreement, 1% at December 31, 2021 (with Alliant Energy as guarantor) (Retired in 2022)
— — — 300 — — 
Corporate Services 3.45% senior notes (Retired in 2022)
— — — 75 — — 
Other, 1% at December 31, 2022, due 2023 to 2025
1 — — 1 — — 
1,668 — — 1,300 — — 
Subtotal8,143 3,675 2,800 7,425 3,675 2,450 
Current maturities(408)— — (633)— (250)
Unamortized debt issuance costs(45)(21)(19)(42)(23)(15)
Unamortized debt (discount) and premium, net(22)(8)(11)(15)(9)(6)
Long-term debt, net (e)$7,668 $3,646 $2,770 $6,735 $3,643 $2,179 

(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 August 2022, WPL issued $600 million of 3.95% debentures due 2032. The debentures were issued as green bonds, and an amount equal to or in excess of the net proceeds were disbursed for the development and acquisition of WPL’s solar EGUs.
(c)In March 2022, AEF entered into a $300 million variable rate term loan credit agreement and used the borrowings under this agreement to retire its $300 million variable rate term loan credit agreement that expired in March 2022. In December 2022, AEF increased the amount outstanding under the new term loan credit agreement by $100 million and used the additional borrowings to reduce Alliant Energy’s outstanding commercial paper and for general corporate purposes. In January 2023, AEF entered into a $300 million interest rate swap maturing in January 2026. Under the terms of the swap, AEF exchanged variable rate borrowings for a fixed rate of 3.93%.
(d)In February 2022, AEF issued $350 million of 3.6% senior notes due 2032. The net proceeds from the issuance were used to reduce Alliant Energy’s outstanding commercial paper and for general corporate purposes.
(e)There were no significant sinking fund requirements related to the outstanding long-term debt.
Schedule of Maturities of Long-term Debt At December 31, 2022, long-term debt maturities for 2023 through 2027 were as follows (in millions):
20232024202520262027
IPL$—$500$300$—$—
WPL————300
AEF408409—200—
Alliant Energy$408$909$300$200$300
WPL [Member]  
Debt Instrument [Line Items]  
Schedule of Other Short-term Borrowings Information regarding Alliant Energy’s, IPL’s and WPL’s commercial paper classified as short-term debt was as follows (dollars in millions):
Alliant EnergyIPLWPL
December 31202220212022202120222021
Amount outstanding$642$515$—$—$290$236
Weighted average interest rates4.6%0.2%N/AN/A4.5%0.2%
Available credit facility capacity$358$485$100$250$110$64
Alliant EnergyIPLWPL
For the year ended202220212022202120222021
Maximum amount outstanding (based on daily outstanding balances)$665$648$—$19$325$320
Average amount outstanding (based on daily outstanding balances)$411$459$—$—$153$172
Weighted average interest rates2.1%0.2%—%0.2%1.6%0.1%
Schedule of Long-term Debt Long-term debt, net as of December 31 was as follows (dollars in millions):
20222021
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
300 300 — 300 300 — 
3,675 3,675 — 3,675 3,675 — 
Debentures (a):
3.05%, due 2027
300 — 300 300 — 300 
3%, due 2029
350 — 350 350 — 350 
1.95%, due 2031
300 — 300 300 — 300 
3.95%, due 2032 (b)
600 — 600 — — — 
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 
2.25% (Retired in 2022)
— — — 250 — 250 
2,800 — 2,800 2,450 — 2,450 
Other:
AEF 3.75% senior notes, due 2023 (with Alliant Energy as guarantor) (a)
400 — — 400 — — 
AEF term loan credit agreement through March 2024, 5% at December 31, 2022 (with Alliant Energy as guarantor) (c)
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 — — 
AEF 3.6% senior notes, due 2032 (with Alliant Energy as guarantor) (a)(d)
350 — — — — — 
Sheboygan Power, LLC 5.06% senior secured notes, due 2023 to 2024 (secured by the Sheboygan Falls Energy Facility and related assets) (a)
17 — — 24 — — 
AEF term loan credit agreement, 1% at December 31, 2021 (with Alliant Energy as guarantor) (Retired in 2022)
— — — 300 — — 
Corporate Services 3.45% senior notes (Retired in 2022)
— — — 75 — — 
Other, 1% at December 31, 2022, due 2023 to 2025
1 — — 1 — — 
1,668 — — 1,300 — — 
Subtotal8,143 3,675 2,800 7,425 3,675 2,450 
Current maturities(408)— — (633)— (250)
Unamortized debt issuance costs(45)(21)(19)(42)(23)(15)
Unamortized debt (discount) and premium, net(22)(8)(11)(15)(9)(6)
Long-term debt, net (e)$7,668 $3,646 $2,770 $6,735 $3,643 $2,179 

(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 August 2022, WPL issued $600 million of 3.95% debentures due 2032. The debentures were issued as green bonds, and an amount equal to or in excess of the net proceeds were disbursed for the development and acquisition of WPL’s solar EGUs.
(c)In March 2022, AEF entered into a $300 million variable rate term loan credit agreement and used the borrowings under this agreement to retire its $300 million variable rate term loan credit agreement that expired in March 2022. In December 2022, AEF increased the amount outstanding under the new term loan credit agreement by $100 million and used the additional borrowings to reduce Alliant Energy’s outstanding commercial paper and for general corporate purposes. In January 2023, AEF entered into a $300 million interest rate swap maturing in January 2026. Under the terms of the swap, AEF exchanged variable rate borrowings for a fixed rate of 3.93%.
(d)In February 2022, AEF issued $350 million of 3.6% senior notes due 2032. The net proceeds from the issuance were used to reduce Alliant Energy’s outstanding commercial paper and for general corporate purposes.
(e)There were no significant sinking fund requirements related to the outstanding long-term debt.
Schedule of Maturities of Long-term Debt At December 31, 2022, long-term debt maturities for 2023 through 2027 were as follows (in millions):
20232024202520262027
IPL$—$500$300$—$—
WPL————300
AEF408409—200—
Alliant Energy$408$909$300$200$300