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Summary of Significant Accounting Policies (Details) - USD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
Summary Of Significant Accounting Policies [Line Items] |  |  |
Foreign currency transaction adjustments | $ (3) | $ (4) | $ (8)
Contributions by employer for employee savings plans | $ 7 | $ 6 | $ 6
Maximum [Member] |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |
Cash and cash equivalents maturity, days | 90 days |  |

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