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Debt | 12 Months Ended
--- | ---
Dec. 31, 2018
Debt Instrument [Line Items] |
Debt | DEBT (a) Short-term Debt - Alliant Energy and its subsidiaries maintain committed bank lines of credit to provide short-term borrowing flexibility and back-stop liquidity for commercial paper outstanding. At December 31, 2018, the short-term borrowing capacity under a single credit facility agreement, which expires in August 2022, totaled $1 billion ($400 million for Alliant Energy at the parent company level, $250 million for IPL and $350 million for WPL). Subject to certain conditions, Alliant Energy (at the parent company level), IPL and WPL may each reallocate and change its sublimit up to $500 million, $400 million and $500 million, respectively, within the $1 billion total commitment. Information regarding commercial paper classified as short-term debt and back-stopped by the credit facility was as follows (dollars in millions):
| Alliant Energy |  | IPL |  | WPL
December 31 | 2018 |  | 2017 |  | 2018 |  | 2017 |  | 2018 |  | 2017
Commercial paper outstanding | $441.2 |  | $320.2 |  | $50.4 |  | $— |  | $105.5 |  | $25.0
Commercial paper weighted average interest rates | 2.8% |  | 2.0% |  | 2.8% |  | N/A |  | 2.5% |  | 1.5%
Available credit facility capacity | $558.8 |  | $679.8 |  | $199.6 |  | $250.0 |  | $244.5 |  | $325.0
| Alliant Energy |  | IPL |  | WPL
For the year ended | 2018 |  | 2017 |  | 2018 |  | 2017 |  | 2018 |  | 2017
Maximum amount outstanding (based on daily outstanding balances) | $446.5 |  | $424.4 |  | $50.4 |  | $20.0 |  | $126.0 |  | $271.2
Average amount outstanding (based on daily outstanding balances) | $221.4 |  | $294.3 |  | $1.5 |  | $0.5 |  | $36.6 |  | $118.2
Weighted average interest rates | 2.2% |  | 1.2% |  | 2.3% |  | 1.3% |  | 2.1% |  | 1.0%
In June 2018, AEF retired its $95 million, 364-day variable-rate (2.2% at December 31, 2017) term loan credit agreement. Financial Covenants - The single credit facility agreement contains a financial covenant, which requires Alliant Energy, IPL and WPL to maintain certain debt-to-capital ratios in order to borrow under the credit facility. AEF’s term loan credit agreement contains a financial covenant, which requires Alliant Energy to maintain a certain debt-to-capital ratio in order to borrow under the term loan credit agreement. The required debt-to-capital ratios compared to the actual debt-to-capital ratios at December 31, 2018 were as follows:
| Alliant Energy |  | IPL |  | WPL
Requirement, not to exceed | 65% |  | 65% |  | 65%
Actual | 55% |  | 45% |  | 48%
The debt component of the capital ratios includes long- and short-term debt (excluding non-recourse debt and hybrid securities to the extent the total carrying value of such hybrid securities does not exceed 15% of consolidated capital of the applicable borrower), capital lease obligations, certain letters of credit, guarantees of the foregoing and new synthetic leases. Unfunded vested benefits under qualified pension plans and sales of accounts receivable are not included in the debt-to-capital ratios. The equity component of the capital ratios excludes accumulated other comprehensive income (loss). (b) Long-Term Debt - Long-term debt, net as of December 31 was as follows (dollars in millions):
| 2018 |  | 2017
| Alliant Energy |  | IPL |  | WPL |  | Alliant Energy |  | IPL |  | WPL
Senior Debentures (a): |  |  |  |  |  |  |  |  |  |  |
3.65%, due 2020 |  | $200.0 |  |  |  | $200.0 |  |  |  | $— |  |  |  | $200.0 |  |  |  | $200.0 |  |  |  | $— |
3.25%, due 2024 | 500.0 |  |  | 500.0 |  |  | — |  |  | 500.0 |  |  | 500.0 |  |  | — |
3.4%, due 2025 | 250.0 |  |  | 250.0 |  |  | — |  |  | 250.0 |  |  | 250.0 |  |  | — |
5.5%, due 2025 | 50.0 |  |  | 50.0 |  |  | — |  |  | 50.0 |  |  | 50.0 |  |  | — |
4.1%, due 2028 (b) | 500.0 |  |  | 500.0 |  |  | — |  |  | — |  |  | — |  |  | — |
6.45%, due 2033 | 100.0 |  |  | 100.0 |  |  | — |  |  | 100.0 |  |  | 100.0 |  |  | — |
6.3%, due 2034 | 125.0 |  |  | 125.0 |  |  | — |  |  | 125.0 |  |  | 125.0 |  |  | — |
6.25%, due 2039 | 300.0 |  |  | 300.0 |  |  | — |  |  | 300.0 |  |  | 300.0 |  |  | — |
4.7%, due 2043 | 250.0 |  |  | 250.0 |  |  | — |  |  | 250.0 |  |  | 250.0 |  |  | — |
3.7%, due 2046 | 300.0 |  |  | 300.0 |  |  | — |  |  | 300.0 |  |  | 300.0 |  |  | — |
5.875% (Retired in 2018) | — |  |  | — |  |  | — |  |  | 100.0 |  |  | 100.0 |  |  | — |
7.25% (Retired in 2018) | — |  |  | — |  |  | — |  |  | 250.0 |  |  | 250.0 |  |  | — |
| 2,575.0 |  |  | 2,575.0 |  |  | — |  |  | 2,425.0 |  |  | 2,425.0 |  |  | — |
Debentures (a): |  |  |  |  |  |  |  |  |  |  |
5%, due 2019 | 250.0 |  |  | — |  |  | 250.0 |  |  | 250.0 |  |  | — |  |  | 250.0 |
4.6%, due 2020 | 150.0 |  |  | — |  |  | 150.0 |  |  | 150.0 |  |  | — |  |  | 150.0 |
2.25%, due 2022 | 250.0 |  |  | — |  |  | 250.0 |  |  | 250.0 |  |  | — |  |  | 250.0 |
3.05%, due 2027 | 300.0 |  |  | — |  |  | 300.0 |  |  | 300.0 |  |  | — |  |  | 300.0 |
6.25%, due 2034 | 100.0 |  |  | — |  |  | 100.0 |  |  | 100.0 |  |  | — |  |  | 100.0 |
6.375%, due 2037 | 300.0 |  |  | — |  |  | 300.0 |  |  | 300.0 |  |  | — |  |  | 300.0 |
7.6%, due 2038 | 250.0 |  |  | — |  |  | 250.0 |  |  | 250.0 |  |  | — |  |  | 250.0 |
4.1%, due 2044 | 250.0 |  |  | — |  |  | 250.0 |  |  | 250.0 |  |  | — |  |  | 250.0 |
| 1,850.0 |  |  | — |  |  | 1,850.0 |  |  | 1,850.0 |  |  | — |  |  | 1,850.0 |
Other: |  |  |  |  |  |  |  |  |  |  |
AEF term loan credit agreement through April 2020, 3% at December 31, 2018 (with Alliant Energy as guarantor) (c) | 300.0 |  |  | — |  |  | — |  |  | — |  |  | — |  |  | — |
Corporate Services 3.45% senior notes, due 2022 (a) | 75.0 |  |  | — |  |  | — |  |  | 75.0 |  |  | — |  |  | — |
AEF 3.75% senior notes, due 2023 (with Alliant Energy as guarantor) (a)(d) | 400.0 |  |  | — |  |  | — |  |  | — |  |  | — |  |  | — |
AEF 4.25% senior notes, due 2028 (with Alliant Energy as guarantor) (a)(d) | 300.0 |  |  | — |  |  | — |  |  | — |  |  | — |  |  | — |
Sheboygan Power, LLC 5.06% senior secured notes, due 2019 to 2024 (secured by the Sheboygan Falls Energy Facility and related assets) (a) | 44.3 |  |  | — |  |  | — |  |  | 49.6 |  |  | — |  |  | — |
AEF term loan credit agreement, 2% at December 31, 2017 (with Alliant Energy as guarantor) (Retired in 2018) (d) | — |  |  | — |  |  | — |  |  | 500.0 |  |  | — |  |  | — |
Other, 1% at December 31, 2018, due 2019 to 2025 | 2.4 |  |  | — |  |  | — |  |  | 2.9 |  |  | — |  |  | — |
| 1,121.7 |  |  | — |  |  | — |  |  | 627.5 |  |  | — |  |  | — |
Subtotal | 5,546.7 |  |  | 2,575.0 |  |  | 1,850.0 |  |  | 4,902.5 |  |  | 2,425.0 |  |  | 1,850.0 |
Current maturities | (256.5 | ) |  | — |  |  | (250.0 | ) |  | (855.7 | ) |  | (350.0 | ) |  | — |
Unamortized debt issuance costs | (32.1 | ) |  | (17.2 | ) |  | (9.6 | ) |  | (25.4 | ) |  | (14.3 | ) |  | (10.5 | )
Unamortized debt (discount) and premium, net | (11.8 | ) |  | (5.5 | ) |  | (5.5 | ) |  | (10.8 | ) |  | (4.7 | ) |  | (6.1 | )
Long-term debt, net (e) |  | $5,246.3 |  |  |  | $2,552.3 |  |  |  | $1,584.9 |  |  |  | $4,010.6 |  |  |  | $2,056.0 |  |  |  | $1,833.4 |
(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 September 2018, IPL issued $500 million of 4.1% senior debentures due 2028. The senior debentures were issued as green bonds, and all of the net proceeds were allocated for the construction and development of wind and solar projects.
(c) | In April 2018, AEF entered into a $300 million variable-rate term loan credit agreement and used the proceeds from borrowings under this agreement for general corporate purposes. Refer to Note 9(a) for discussion of a financial covenant contained in AEF’s term loan credit agreement.
(d) | In June 2018, AEF issued $400 million of 3.75% senior notes due 2023 and $300 million of 4.25% senior notes due 2028. The proceeds from the issuances were used by AEF to retire its $500 million and $95 million variable-rate term loan credit agreements expiring in 2018, 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.
Five-Year Schedule of Long-term Debt Maturities - At December 31, 2018, long-term debt maturities for 2019 through 2023 were as follows (in millions):
| 2019 |  | 2020 |  | 2021 |  | 2022 |  | 2023
IPL |  | $— |  |  |  | $200 |  |  |  | $— |  |  |  | $— |  |  |  | $— |
WPL | 250 |  |  | 150 |  |  | — |  |  | 250 |  |  | — |
Corporate Services | — |  |  | — |  |  | — |  |  | 75 |  |  | — |
AEF | 6 |  |  | 307 |  |  | 8 |  |  | 8 |  |  | 408 |
Alliant Energy |  | $256 |  |  |  | $657 |  |  |  | $8 |  |  |  | $333 |  |  |  | $408 |
Fair Value of Long-term Debt - Refer to Note 16 for information on the fair value of long-term debt outstanding.
IPL [Member] |
Debt Instrument [Line Items] |
Debt | DEBT (a) Short-term Debt - Alliant Energy and its subsidiaries maintain committed bank lines of credit to provide short-term borrowing flexibility and back-stop liquidity for commercial paper outstanding. At December 31, 2018, the short-term borrowing capacity under a single credit facility agreement, which expires in August 2022, totaled $1 billion ($400 million for Alliant Energy at the parent company level, $250 million for IPL and $350 million for WPL). Subject to certain conditions, Alliant Energy (at the parent company level), IPL and WPL may each reallocate and change its sublimit up to $500 million, $400 million and $500 million, respectively, within the $1 billion total commitment. Information regarding commercial paper classified as short-term debt and back-stopped by the credit facility was as follows (dollars in millions):
| Alliant Energy |  | IPL |  | WPL
December 31 | 2018 |  | 2017 |  | 2018 |  | 2017 |  | 2018 |  | 2017
Commercial paper outstanding | $441.2 |  | $320.2 |  | $50.4 |  | $— |  | $105.5 |  | $25.0
Commercial paper weighted average interest rates | 2.8% |  | 2.0% |  | 2.8% |  | N/A |  | 2.5% |  | 1.5%
Available credit facility capacity | $558.8 |  | $679.8 |  | $199.6 |  | $250.0 |  | $244.5 |  | $325.0
| Alliant Energy |  | IPL |  | WPL
For the year ended | 2018 |  | 2017 |  | 2018 |  | 2017 |  | 2018 |  | 2017
Maximum amount outstanding (based on daily outstanding balances) | $446.5 |  | $424.4 |  | $50.4 |  | $20.0 |  | $126.0 |  | $271.2
Average amount outstanding (based on daily outstanding balances) | $221.4 |  | $294.3 |  | $1.5 |  | $0.5 |  | $36.6 |  | $118.2
Weighted average interest rates | 2.2% |  | 1.2% |  | 2.3% |  | 1.3% |  | 2.1% |  | 1.0%
In June 2018, AEF retired its $95 million, 364-day variable-rate (2.2% at December 31, 2017) term loan credit agreement. Financial Covenants - The single credit facility agreement contains a financial covenant, which requires Alliant Energy, IPL and WPL to maintain certain debt-to-capital ratios in order to borrow under the credit facility. AEF’s term loan credit agreement contains a financial covenant, which requires Alliant Energy to maintain a certain debt-to-capital ratio in order to borrow under the term loan credit agreement. The required debt-to-capital ratios compared to the actual debt-to-capital ratios at December 31, 2018 were as follows:
| Alliant Energy |  | IPL |  | WPL
Requirement, not to exceed | 65% |  | 65% |  | 65%
Actual | 55% |  | 45% |  | 48%
The debt component of the capital ratios includes long- and short-term debt (excluding non-recourse debt and hybrid securities to the extent the total carrying value of such hybrid securities does not exceed 15% of consolidated capital of the applicable borrower), capital lease obligations, certain letters of credit, guarantees of the foregoing and new synthetic leases. Unfunded vested benefits under qualified pension plans and sales of accounts receivable are not included in the debt-to-capital ratios. The equity component of the capital ratios excludes accumulated other comprehensive income (loss). (b) Long-Term Debt - Long-term debt, net as of December 31 was as follows (dollars in millions):
| 2018 |  | 2017
| Alliant Energy |  | IPL |  | WPL |  | Alliant Energy |  | IPL |  | WPL
Senior Debentures (a): |  |  |  |  |  |  |  |  |  |  |
3.65%, due 2020 |  | $200.0 |  |  |  | $200.0 |  |  |  | $— |  |  |  | $200.0 |  |  |  | $200.0 |  |  |  | $— |
3.25%, due 2024 | 500.0 |  |  | 500.0 |  |  | — |  |  | 500.0 |  |  | 500.0 |  |  | — |
3.4%, due 2025 | 250.0 |  |  | 250.0 |  |  | — |  |  | 250.0 |  |  | 250.0 |  |  | — |
5.5%, due 2025 | 50.0 |  |  | 50.0 |  |  | — |  |  | 50.0 |  |  | 50.0 |  |  | — |
4.1%, due 2028 (b) | 500.0 |  |  | 500.0 |  |  | — |  |  | — |  |  | — |  |  | — |
6.45%, due 2033 | 100.0 |  |  | 100.0 |  |  | — |  |  | 100.0 |  |  | 100.0 |  |  | — |
6.3%, due 2034 | 125.0 |  |  | 125.0 |  |  | — |  |  | 125.0 |  |  | 125.0 |  |  | — |
6.25%, due 2039 | 300.0 |  |  | 300.0 |  |  | — |  |  | 300.0 |  |  | 300.0 |  |  | — |
4.7%, due 2043 | 250.0 |  |  | 250.0 |  |  | — |  |  | 250.0 |  |  | 250.0 |  |  | — |
3.7%, due 2046 | 300.0 |  |  | 300.0 |  |  | — |  |  | 300.0 |  |  | 300.0 |  |  | — |
5.875% (Retired in 2018) | — |  |  | — |  |  | — |  |  | 100.0 |  |  | 100.0 |  |  | — |
7.25% (Retired in 2018) | — |  |  | — |  |  | — |  |  | 250.0 |  |  | 250.0 |  |  | — |
| 2,575.0 |  |  | 2,575.0 |  |  | — |  |  | 2,425.0 |  |  | 2,425.0 |  |  | — |
Debentures (a): |  |  |  |  |  |  |  |  |  |  |
5%, due 2019 | 250.0 |  |  | — |  |  | 250.0 |  |  | 250.0 |  |  | — |  |  | 250.0 |
4.6%, due 2020 | 150.0 |  |  | — |  |  | 150.0 |  |  | 150.0 |  |  | — |  |  | 150.0 |
2.25%, due 2022 | 250.0 |  |  | — |  |  | 250.0 |  |  | 250.0 |  |  | — |  |  | 250.0 |
3.05%, due 2027 | 300.0 |  |  | — |  |  | 300.0 |  |  | 300.0 |  |  | — |  |  | 300.0 |
6.25%, due 2034 | 100.0 |  |  | — |  |  | 100.0 |  |  | 100.0 |  |  | — |  |  | 100.0 |
6.375%, due 2037 | 300.0 |  |  | — |  |  | 300.0 |  |  | 300.0 |  |  | — |  |  | 300.0 |
7.6%, due 2038 | 250.0 |  |  | — |  |  | 250.0 |  |  | 250.0 |  |  | — |  |  | 250.0 |
4.1%, due 2044 | 250.0 |  |  | — |  |  | 250.0 |  |  | 250.0 |  |  | — |  |  | 250.0 |
| 1,850.0 |  |  | — |  |  | 1,850.0 |  |  | 1,850.0 |  |  | — |  |  | 1,850.0 |
Other: |  |  |  |  |  |  |  |  |  |  |
AEF term loan credit agreement through April 2020, 3% at December 31, 2018 (with Alliant Energy as guarantor) (c) | 300.0 |  |  | — |  |  | — |  |  | — |  |  | — |  |  | — |
Corporate Services 3.45% senior notes, due 2022 (a) | 75.0 |  |  | — |  |  | — |  |  | 75.0 |  |  | — |  |  | — |
AEF 3.75% senior notes, due 2023 (with Alliant Energy as guarantor) (a)(d) | 400.0 |  |  | — |  |  | — |  |  | — |  |  | — |  |  | — |
AEF 4.25% senior notes, due 2028 (with Alliant Energy as guarantor) (a)(d) | 300.0 |  |  | — |  |  | — |  |  | — |  |  | — |  |  | — |
Sheboygan Power, LLC 5.06% senior secured notes, due 2019 to 2024 (secured by the Sheboygan Falls Energy Facility and related assets) (a) | 44.3 |  |  | — |  |  | — |  |  | 49.6 |  |  | — |  |  | — |
AEF term loan credit agreement, 2% at December 31, 2017 (with Alliant Energy as guarantor) (Retired in 2018) (d) | — |  |  | — |  |  | — |  |  | 500.0 |  |  | — |  |  | — |
Other, 1% at December 31, 2018, due 2019 to 2025 | 2.4 |  |  | — |  |  | — |  |  | 2.9 |  |  | — |  |  | — |
| 1,121.7 |  |  | — |  |  | — |  |  | 627.5 |  |  | — |  |  | — |
Subtotal | 5,546.7 |  |  | 2,575.0 |  |  | 1,850.0 |  |  | 4,902.5 |  |  | 2,425.0 |  |  | 1,850.0 |
Current maturities | (256.5 | ) |  | — |  |  | (250.0 | ) |  | (855.7 | ) |  | (350.0 | ) |  | — |
Unamortized debt issuance costs | (32.1 | ) |  | (17.2 | ) |  | (9.6 | ) |  | (25.4 | ) |  | (14.3 | ) |  | (10.5 | )
Unamortized debt (discount) and premium, net | (11.8 | ) |  | (5.5 | ) |  | (5.5 | ) |  | (10.8 | ) |  | (4.7 | ) |  | (6.1 | )
Long-term debt, net (e) |  | $5,246.3 |  |  |  | $2,552.3 |  |  |  | $1,584.9 |  |  |  | $4,010.6 |  |  |  | $2,056.0 |  |  |  | $1,833.4 |
(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 September 2018, IPL issued $500 million of 4.1% senior debentures due 2028. The senior debentures were issued as green bonds, and all of the net proceeds were allocated for the construction and development of wind and solar projects.
(c) | In April 2018, AEF entered into a $300 million variable-rate term loan credit agreement and used the proceeds from borrowings under this agreement for general corporate purposes. Refer to Note 9(a) for discussion of a financial covenant contained in AEF’s term loan credit agreement.
(d) | In June 2018, AEF issued $400 million of 3.75% senior notes due 2023 and $300 million of 4.25% senior notes due 2028. The proceeds from the issuances were used by AEF to retire its $500 million and $95 million variable-rate term loan credit agreements expiring in 2018, 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.
Five-Year Schedule of Long-term Debt Maturities - At December 31, 2018, long-term debt maturities for 2019 through 2023 were as follows (in millions):
| 2019 |  | 2020 |  | 2021 |  | 2022 |  | 2023
IPL |  | $— |  |  |  | $200 |  |  |  | $— |  |  |  | $— |  |  |  | $— |
WPL | 250 |  |  | 150 |  |  | — |  |  | 250 |  |  | — |
Corporate Services | — |  |  | — |  |  | — |  |  | 75 |  |  | — |
AEF | 6 |  |  | 307 |  |  | 8 |  |  | 8 |  |  | 408 |
Alliant Energy |  | $256 |  |  |  | $657 |  |  |  | $8 |  |  |  | $333 |  |  |  | $408 |
Fair Value of Long-term Debt - Refer to Note 16 for information on the fair value of long-term debt outstanding.
WPL [Member] |
Debt Instrument [Line Items] |
Debt | DEBT (a) Short-term Debt - Alliant Energy and its subsidiaries maintain committed bank lines of credit to provide short-term borrowing flexibility and back-stop liquidity for commercial paper outstanding. At December 31, 2018, the short-term borrowing capacity under a single credit facility agreement, which expires in August 2022, totaled $1 billion ($400 million for Alliant Energy at the parent company level, $250 million for IPL and $350 million for WPL). Subject to certain conditions, Alliant Energy (at the parent company level), IPL and WPL may each reallocate and change its sublimit up to $500 million, $400 million and $500 million, respectively, within the $1 billion total commitment. Information regarding commercial paper classified as short-term debt and back-stopped by the credit facility was as follows (dollars in millions):
| Alliant Energy |  | IPL |  | WPL
December 31 | 2018 |  | 2017 |  | 2018 |  | 2017 |  | 2018 |  | 2017
Commercial paper outstanding | $441.2 |  | $320.2 |  | $50.4 |  | $— |  | $105.5 |  | $25.0
Commercial paper weighted average interest rates | 2.8% |  | 2.0% |  | 2.8% |  | N/A |  | 2.5% |  | 1.5%
Available credit facility capacity | $558.8 |  | $679.8 |  | $199.6 |  | $250.0 |  | $244.5 |  | $325.0
| Alliant Energy |  | IPL |  | WPL
For the year ended | 2018 |  | 2017 |  | 2018 |  | 2017 |  | 2018 |  | 2017
Maximum amount outstanding (based on daily outstanding balances) | $446.5 |  | $424.4 |  | $50.4 |  | $20.0 |  | $126.0 |  | $271.2
Average amount outstanding (based on daily outstanding balances) | $221.4 |  | $294.3 |  | $1.5 |  | $0.5 |  | $36.6 |  | $118.2
Weighted average interest rates | 2.2% |  | 1.2% |  | 2.3% |  | 1.3% |  | 2.1% |  | 1.0%
In June 2018, AEF retired its $95 million, 364-day variable-rate (2.2% at December 31, 2017) term loan credit agreement. Financial Covenants - The single credit facility agreement contains a financial covenant, which requires Alliant Energy, IPL and WPL to maintain certain debt-to-capital ratios in order to borrow under the credit facility. AEF’s term loan credit agreement contains a financial covenant, which requires Alliant Energy to maintain a certain debt-to-capital ratio in order to borrow under the term loan credit agreement. The required debt-to-capital ratios compared to the actual debt-to-capital ratios at December 31, 2018 were as follows:
| Alliant Energy |  | IPL |  | WPL
Requirement, not to exceed | 65% |  | 65% |  | 65%
Actual | 55% |  | 45% |  | 48%
The debt component of the capital ratios includes long- and short-term debt (excluding non-recourse debt and hybrid securities to the extent the total carrying value of such hybrid securities does not exceed 15% of consolidated capital of the applicable borrower), capital lease obligations, certain letters of credit, guarantees of the foregoing and new synthetic leases. Unfunded vested benefits under qualified pension plans and sales of accounts receivable are not included in the debt-to-capital ratios. The equity component of the capital ratios excludes accumulated other comprehensive income (loss). (b) Long-Term Debt - Long-term debt, net as of December 31 was as follows (dollars in millions):
| 2018 |  | 2017
| Alliant Energy |  | IPL |  | WPL |  | Alliant Energy |  | IPL |  | WPL
Senior Debentures (a): |  |  |  |  |  |  |  |  |  |  |
3.65%, due 2020 |  | $200.0 |  |  |  | $200.0 |  |  |  | $— |  |  |  | $200.0 |  |  |  | $200.0 |  |  |  | $— |
3.25%, due 2024 | 500.0 |  |  | 500.0 |  |  | — |  |  | 500.0 |  |  | 500.0 |  |  | — |
3.4%, due 2025 | 250.0 |  |  | 250.0 |  |  | — |  |  | 250.0 |  |  | 250.0 |  |  | — |
5.5%, due 2025 | 50.0 |  |  | 50.0 |  |  | — |  |  | 50.0 |  |  | 50.0 |  |  | — |
4.1%, due 2028 (b) | 500.0 |  |  | 500.0 |  |  | — |  |  | — |  |  | — |  |  | — |
6.45%, due 2033 | 100.0 |  |  | 100.0 |  |  | — |  |  | 100.0 |  |  | 100.0 |  |  | — |
6.3%, due 2034 | 125.0 |  |  | 125.0 |  |  | — |  |  | 125.0 |  |  | 125.0 |  |  | — |
6.25%, due 2039 | 300.0 |  |  | 300.0 |  |  | — |  |  | 300.0 |  |  | 300.0 |  |  | — |
4.7%, due 2043 | 250.0 |  |  | 250.0 |  |  | — |  |  | 250.0 |  |  | 250.0 |  |  | — |
3.7%, due 2046 | 300.0 |  |  | 300.0 |  |  | — |  |  | 300.0 |  |  | 300.0 |  |  | — |
5.875% (Retired in 2018) | — |  |  | — |  |  | — |  |  | 100.0 |  |  | 100.0 |  |  | — |
7.25% (Retired in 2018) | — |  |  | — |  |  | — |  |  | 250.0 |  |  | 250.0 |  |  | — |
| 2,575.0 |  |  | 2,575.0 |  |  | — |  |  | 2,425.0 |  |  | 2,425.0 |  |  | — |
Debentures (a): |  |  |  |  |  |  |  |  |  |  |
5%, due 2019 | 250.0 |  |  | — |  |  | 250.0 |  |  | 250.0 |  |  | — |  |  | 250.0 |
4.6%, due 2020 | 150.0 |  |  | — |  |  | 150.0 |  |  | 150.0 |  |  | — |  |  | 150.0 |
2.25%, due 2022 | 250.0 |  |  | — |  |  | 250.0 |  |  | 250.0 |  |  | — |  |  | 250.0 |
3.05%, due 2027 | 300.0 |  |  | — |  |  | 300.0 |  |  | 300.0 |  |  | — |  |  | 300.0 |
6.25%, due 2034 | 100.0 |  |  | — |  |  | 100.0 |  |  | 100.0 |  |  | — |  |  | 100.0 |
6.375%, due 2037 | 300.0 |  |  | — |  |  | 300.0 |  |  | 300.0 |  |  | — |  |  | 300.0 |
7.6%, due 2038 | 250.0 |  |  | — |  |  | 250.0 |  |  | 250.0 |  |  | — |  |  | 250.0 |
4.1%, due 2044 | 250.0 |  |  | — |  |  | 250.0 |  |  | 250.0 |  |  | — |  |  | 250.0 |
| 1,850.0 |  |  | — |  |  | 1,850.0 |  |  | 1,850.0 |  |  | — |  |  | 1,850.0 |
Other: |  |  |  |  |  |  |  |  |  |  |
AEF term loan credit agreement through April 2020, 3% at December 31, 2018 (with Alliant Energy as guarantor) (c) | 300.0 |  |  | — |  |  | — |  |  | — |  |  | — |  |  | — |
Corporate Services 3.45% senior notes, due 2022 (a) | 75.0 |  |  | — |  |  | — |  |  | 75.0 |  |  | — |  |  | — |
AEF 3.75% senior notes, due 2023 (with Alliant Energy as guarantor) (a)(d) | 400.0 |  |  | — |  |  | — |  |  | — |  |  | — |  |  | — |
AEF 4.25% senior notes, due 2028 (with Alliant Energy as guarantor) (a)(d) | 300.0 |  |  | — |  |  | — |  |  | — |  |  | — |  |  | — |
Sheboygan Power, LLC 5.06% senior secured notes, due 2019 to 2024 (secured by the Sheboygan Falls Energy Facility and related assets) (a) | 44.3 |  |  | — |  |  | — |  |  | 49.6 |  |  | — |  |  | — |
AEF term loan credit agreement, 2% at December 31, 2017 (with Alliant Energy as guarantor) (Retired in 2018) (d) | — |  |  | — |  |  | — |  |  | 500.0 |  |  | — |  |  | — |
Other, 1% at December 31, 2018, due 2019 to 2025 | 2.4 |  |  | — |  |  | — |  |  | 2.9 |  |  | — |  |  | — |
| 1,121.7 |  |  | — |  |  | — |  |  | 627.5 |  |  | — |  |  | — |
Subtotal | 5,546.7 |  |  | 2,575.0 |  |  | 1,850.0 |  |  | 4,902.5 |  |  | 2,425.0 |  |  | 1,850.0 |
Current maturities | (256.5 | ) |  | — |  |  | (250.0 | ) |  | (855.7 | ) |  | (350.0 | ) |  | — |
Unamortized debt issuance costs | (32.1 | ) |  | (17.2 | ) |  | (9.6 | ) |  | (25.4 | ) |  | (14.3 | ) |  | (10.5 | )
Unamortized debt (discount) and premium, net | (11.8 | ) |  | (5.5 | ) |  | (5.5 | ) |  | (10.8 | ) |  | (4.7 | ) |  | (6.1 | )
Long-term debt, net (e) |  | $5,246.3 |  |  |  | $2,552.3 |  |  |  | $1,584.9 |  |  |  | $4,010.6 |  |  |  | $2,056.0 |  |  |  | $1,833.4 |
(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 September 2018, IPL issued $500 million of 4.1% senior debentures due 2028. The senior debentures were issued as green bonds, and all of the net proceeds were allocated for the construction and development of wind and solar projects.
(c) | In April 2018, AEF entered into a $300 million variable-rate term loan credit agreement and used the proceeds from borrowings under this agreement for general corporate purposes. Refer to Note 9(a) for discussion of a financial covenant contained in AEF’s term loan credit agreement.
(d) | In June 2018, AEF issued $400 million of 3.75% senior notes due 2023 and $300 million of 4.25% senior notes due 2028. The proceeds from the issuances were used by AEF to retire its $500 million and $95 million variable-rate term loan credit agreements expiring in 2018, 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.
Five-Year Schedule of Long-term Debt Maturities - At December 31, 2018, long-term debt maturities for 2019 through 2023 were as follows (in millions):
| 2019 |  | 2020 |  | 2021 |  | 2022 |  | 2023
IPL |  | $— |  |  |  | $200 |  |  |  | $— |  |  |  | $— |  |  |  | $— |
WPL | 250 |  |  | 150 |  |  | — |  |  | 250 |  |  | — |
Corporate Services | — |  |  | — |  |  | — |  |  | 75 |  |  | — |
AEF | 6 |  |  | 307 |  |  | 8 |  |  | 8 |  |  | 408 |
Alliant Energy |  | $256 |  |  |  | $657 |  |  |  | $8 |  |  |  | $333 |  |  |  | $408 |
Fair Value of Long-term Debt - Refer to Note 16 for information on the fair value of long-term debt outstanding.

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