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Summary of Significant Accounting Policies (Tables) | 9 Months Ended
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Sep. 30, 2021
Accounting Policies [Abstract] |
Allowance for doubtful accounts receivable | The following table provides a rollforward of changes in the allowance for doubtful accounts:
| Nine Months Ended September 30,
(In millions) | 2021 |  | 2020
Beginning balance | $ | 4 |  |  | $ | 10 |
Provision | 1 |  |  | 2 |
Recoveries | — |  |  | (3) |
Write-offs charged against the allowance | — |  |  | (4) |
Ending balance | $ | 5 |  |  | $ | 5 |

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- Definition Tabular disclosure of allowance for credit loss on financing receivable. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 11B -URI http://asc.fasb.org/extlink&oid=121611835&loc=SL6953423-111524 Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 20 -Section 50 -Paragraph 13 -URI http://asc.fasb.org/extlink&oid=121599337&loc=SL82919249-210447 + Details
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