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Summary Of Significant Accounting Policies (Narrative) (Details) - USD ($) $ in Millions | Jun. 30, 2020 | Dec. 31, 2019
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New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |
Money market fund investments | $ 198.3 | $ 5.4
Money market fund investments interest rate, percentage | 0.10% |
IPL [Member] |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |
Money market fund investments | $ 198.3 | 5.4
Money market fund investments interest rate, percentage | 0.10% |
Credit Losses ASU [Member] |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |
New accounting standard, cumulative effect adjustment to retained earnings, pre-tax |  | 12.0
New accounting standard, cumulative effect adjustment to retained earnings, after-tax |  | $ 8.7

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