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Commitments And Contingencies (Narrative) (Details) - USD ($) $ in Millions | 1 Months Ended | 3 Months Ended | 9 Months Ended | 12 Months Ended |
--- | --- | --- | --- | --- | ---
May 31, 2020 | Sep. 30, 2020 | Sep. 30, 2020 | Dec. 31, 2019 | Mar. 31, 2020
Commitments and Contingencies [Line Items] |  |  |  |  |
Minimum future commitments |  |  | $ 1,219 |  |
IPL [Member] |  |  |  |  |
Commitments and Contingencies [Line Items] |  |  |  |  |
Minimum future commitments |  |  | 627 |  |
WPL [Member] |  |  |  |  |
Commitments and Contingencies [Line Items] |  |  |  |  |
Minimum future commitments |  |  | 561 |  |
Capital Purchase Commitment [Member] |  |  |  |  |
Commitments and Contingencies [Line Items] |  |  |  |  |
Minimum future commitments |  |  | 21 |  |
Capital Purchase Commitment [Member] | WPL [Member] |  |  |  |  |
Commitments and Contingencies [Line Items] |  |  |  |  |
Minimum future commitments |  |  | 18 |  |
Indemnification Agreement [Member] |  |  |  |  |
Commitments and Contingencies [Line Items] |  |  |  |  |
Obligations, maximum |  | $ 74 | 74 |  |
Indemnification Agreement [Member] | IPL [Member] |  |  |  |  |
Commitments and Contingencies [Line Items] |  |  |  |  |
Obligations, maximum |  | 17 | 17 |  |
Indemnification Agreement [Member] | Purchased Power [Member] |  |  |  |  |
Commitments and Contingencies [Line Items] |  |  |  |  |
Obligations, maximum |  | 17 | $ 17 |  |
Credit Losses ASU [Member] |  |  |  |  |
Commitments and Contingencies [Line Items] |  |  |  |  |
New accounting standard, cumulative effect adjustment to retained earnings, pre-tax |  |  |  | $ 12 |
Whiting Petroleum Affiliate [Member] |  |  |  |  |
Commitments and Contingencies [Line Items] |  |  |  |  |
Partnership share, percent |  |  | 6.00% |  |
Obligations, maximum |  | 68 | $ 68 |  |
Credit loss liability |  | 5 | 5 |  | $ 20
Credit loss expense |  | $ 15 | 7 |  |
Whiting Petroleum Affiliate [Member] | Credit Losses ASU [Member] |  |  |  |  |
Commitments and Contingencies [Line Items] |  |  |  |  |
New accounting standard, cumulative effect adjustment to retained earnings, pre-tax |  |  |  | $ 12 |
FederalEnergyRegulatoryCommission [Member] |  |  |  |  |
Commitments and Contingencies [Line Items] |  |  |  |  |
MISO base return on equity, percentage | 10.02% |  |  | 9.88% |
FederalEnergyRegulatoryCommission [Member] | IPL [Member] |  |  |  |  |
Commitments and Contingencies [Line Items] |  |  |  |  |
Refunds related to MISO base return on equity complaints |  |  | 15 |  |
FederalEnergyRegulatoryCommission [Member] | WPL [Member] |  |  |  |  |
Commitments and Contingencies [Line Items] |  |  |  |  |
Refunds related to MISO base return on equity complaints |  |  | $ 5 |  |

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- Definition Maximum potential amount of future payments (undiscounted) the guarantor could be required to make under the guarantee or each group of similar guarantees before reduction for potential recoveries under recourse or collateralization provisions. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 460 -SubTopic 10 -Section 50 -Paragraph 4 -Subparagraph (b)(1) -URI http://asc.fasb.org/extlink&oid=118943654&loc=d3e12069-110248 + Details
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- Definition Percentage investment held by members or limited partners of limited liability company (LLC) or limited partnership (LP). + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 272 -SubTopic 10 -Section 50 -Paragraph 3 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=6373374&loc=d3e70478-108055 + Details
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- Definition Amount of expected credit loss for credit exposure on off-balance-sheet commitment, including but not limited to, loan commitment, standby letter of credit, financial guarantee not accounted for as insurance. Excludes off-balance sheet credit exposure accounted for as insurance and instrument accounted for under derivatives and hedging. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 460 -SubTopic 10 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=118956080&loc=d3e11927-110247 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 20 -Section 45 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=118955202&loc=SL82919202-210446 + Details
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