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Commitments And Contingencies (Narrative) (Details) $ in Millions | 12 Months Ended
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Dec. 31, 2017 USD ($)
Long-term Purchase Commitment [Line Items] |  |
Minimum future commitments | $ 2,410 |
Present value abandonment obligation | 33 |
Purchased Power [Member] |  |
Long-term Purchase Commitment [Line Items] |  |
Minimum future commitments | 1,232 | [1]
Capital Purchase Obligation [Member] |  |
Long-term Purchase Commitment [Line Items] |  |
Minimum future commitments | 82 |
IPL [Member] |  |
Long-term Purchase Commitment [Line Items] |  |
Minimum future commitments | 1,669 |
Maximum indemnification limit | 17 |
IPL [Member] | Purchased Power [Member] |  |
Long-term Purchase Commitment [Line Items] |  |
Minimum future commitments | 1,159 | [1]
IPL [Member] | Capital Purchase Obligation [Member] |  |
Long-term Purchase Commitment [Line Items] |  |
Minimum future commitments | 15 |
WPL [Member] |  |
Long-term Purchase Commitment [Line Items] |  |
Minimum future commitments | 735 |
WPL [Member] | Purchased Power [Member] |  |
Long-term Purchase Commitment [Line Items] |  |
Minimum future commitments | 73 | [1]
WPL [Member] | Capital Purchase Obligation [Member] |  |
Long-term Purchase Commitment [Line Items] |  |
Minimum future commitments | 67 |
Indemnification Agreement [Member] |  |
Long-term Purchase Commitment [Line Items] |  |
Maximum indemnification limit | 98 |
Indemnification Agreement [Member] | Purchased Power [Member] |  |
Long-term Purchase Commitment [Line Items] |  |
Maximum indemnification limit | $ 17 |
[1] | Includes payments required by PPAs for capacity rights and minimum quantities of MWhs required to be purchased.

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Balance Type: | credit
Period Type: | instant

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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://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 460 -SubTopic 10 -Section 50 -Paragraph 4 -Subparagraph (b)(1) -URI http://asc.fasb.org/extlink&oid=6851643&loc=d3e12069-110248 + Details
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- Definition The minimum amount the entity agreed to spend under the long-term purchase commitment. + References No definition available. + Details
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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
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- Details
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- Details
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- Details
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