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Debt | 3 Months Ended
--- | ---
Mar. 31, 2021
Debt [Line Items] |
Debt | DEBT Short-term Debt - 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, which currently expires in August 2023, classified as short-term debt was as follows (dollars in millions):
March 31, 2021 | Alliant Energy |  | IPL |  | WPL
Amount outstanding | $336 |  | $— |  | $148
Weighted average interest rates | 0.2% |  | N/A |  | 0.1%
Available credit facility capacity | $664 |  | $250 |  | $152
| Alliant Energy |  | IPL |  | WPL
Three Months Ended March 31 | 2021 |  | 2020 |  | 2021 |  | 2020 |  | 2021 |  | 2020
Maximum amount outstanding (based on daily outstanding balances) | $578 |  | $463 |  | $— |  | $1 |  | $275 |  | $212
Average amount outstanding (based on daily outstanding balances) | $424 |  | $382 |  | $— |  | $— |  | $189 |  | $167
Weighted average interest rates | 0.2% |  | 1.8% |  | —% |  | 1.8% |  | 0.2% |  | 1.8%
IPL [Member] |
Debt [Line Items] |
Debt | DEBT Short-term Debt - 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, which currently expires in August 2023, classified as short-term debt was as follows (dollars in millions):
March 31, 2021 | Alliant Energy |  | IPL |  | WPL
Amount outstanding | $336 |  | $— |  | $148
Weighted average interest rates | 0.2% |  | N/A |  | 0.1%
Available credit facility capacity | $664 |  | $250 |  | $152
| Alliant Energy |  | IPL |  | WPL
Three Months Ended March 31 | 2021 |  | 2020 |  | 2021 |  | 2020 |  | 2021 |  | 2020
Maximum amount outstanding (based on daily outstanding balances) | $578 |  | $463 |  | $— |  | $1 |  | $275 |  | $212
Average amount outstanding (based on daily outstanding balances) | $424 |  | $382 |  | $— |  | $— |  | $189 |  | $167
Weighted average interest rates | 0.2% |  | 1.8% |  | —% |  | 1.8% |  | 0.2% |  | 1.8%
WPL [Member] |
Debt [Line Items] |
Debt | DEBT Short-term Debt - 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, which currently expires in August 2023, classified as short-term debt was as follows (dollars in millions):
March 31, 2021 | Alliant Energy |  | IPL |  | WPL
Amount outstanding | $336 |  | $— |  | $148
Weighted average interest rates | 0.2% |  | N/A |  | 0.1%
Available credit facility capacity | $664 |  | $250 |  | $152
| Alliant Energy |  | IPL |  | WPL
Three Months Ended March 31 | 2021 |  | 2020 |  | 2021 |  | 2020 |  | 2021 |  | 2020
Maximum amount outstanding (based on daily outstanding balances) | $578 |  | $463 |  | $— |  | $1 |  | $275 |  | $212
Average amount outstanding (based on daily outstanding balances) | $424 |  | $382 |  | $— |  | $— |  | $189 |  | $167
Weighted average interest rates | 0.2% |  | 1.8% |  | —% |  | 1.8% |  | 0.2% |  | 1.8%

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- Definition The entire disclosure for information about short-term and long-term debt arrangements, which includes amounts of borrowings under each line of credit, note payable, commercial paper issue, bonds indenture, debenture issue, own-share lending arrangements and any other contractual agreement to repay funds, and about the underlying arrangements, rationale for a classification as long-term, including repayment terms, interest rates, collateral provided, restrictions on use of assets and activities, whether or not in compliance with debt covenants, and other matters important to users of the financial statements, such as the effects of refinancing and noncompliance with debt covenants. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 470 -URI http://asc.fasb.org/topic&trid=2208564 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 470 -SubTopic 20 -Section 50 -Paragraph 1B -Subparagraph (h) -URI http://asc.fasb.org/extlink&oid=123466505&loc=SL123495323-112611 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 470 -SubTopic 20 -Section 50 -Paragraph 1C -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=123466505&loc=SL123495334-112611 Reference 4: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 470 -SubTopic 20 -Section 50 -Paragraph 1I -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=123466505&loc=SL123495371-112611 Reference 5: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 470 -SubTopic 20 -Section 50 -Paragraph 1I -Subparagraph (d) -URI http://asc.fasb.org/extlink&oid=123466505&loc=SL123495371-112611 Reference 6: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 235 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.4-08(c)) -URI http://asc.fasb.org/extlink&oid=120395691&loc=d3e23780-122690 Reference 7: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 470 -SubTopic 20 -Section 50 -Paragraph 1B -Subparagraph (g) -URI http://asc.fasb.org/extlink&oid=123466505&loc=SL123495323-112611 Reference 8: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 470 -SubTopic 20 -Section 50 -Paragraph 1C -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=123466505&loc=SL123495334-112611 Reference 9: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 470 -SubTopic 20 -Section 50 -Paragraph 1C -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=123466505&loc=SL123495334-112611 Reference 10: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 470 -SubTopic 20 -Section 50 -Paragraph 1E -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=123466505&loc=SL123495348-112611 Reference 11: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 470 -SubTopic 20 -Section 50 -Paragraph 1B -URI http://asc.fasb.org/extlink&oid=123466505&loc=SL123495323-112611 Reference 12: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 470 -SubTopic 20 -Section 50 -Paragraph 1I -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=123466505&loc=SL123495371-112611 Reference 13: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 470 -SubTopic 20 -Section 50 -Paragraph 1B -Subparagraph (i) -URI http://asc.fasb.org/extlink&oid=123466505&loc=SL123495323-112611 + Details
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