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Marketable Securities - Additional Information (Detail) - USD ($) $ in Millions | 12 Months Ended |
--- | --- | ---
Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2017
Financing Receivable, Recorded Investment [Line Items] |  |  |
Marketable securities | $ 133 | $ 330 | $ 431
Proceeds from matured marketable securities | 200 | 100 |
U.S. Treasury Debt Securities [Member] |  |  |
Financing Receivable, Recorded Investment [Line Items] |  |  |
Marketable securities | 133 | 330 | $ 431
Proceeds from matured marketable securities | $ 200 | $ 100 |
Weighted average maturity period | 1 year 6 months |  |
Aggregate amortized cost basis of securities | $ 132 |  |

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