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Interest Income (Expense), Net - Additional Information (Detail) - USD ($) | 12 Months Ended
--- | ---
Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
Net Investment Income [Line Items] |  |  |
Capitalized borrowing cost | $ 0 | $ 0 | $ 0
U.S. Treasury Bonds [Member] |  |  |
Net Investment Income [Line Items] |  |  |
Interest income (expense), net | 3,000,000 | 6,000,000 | 6,000,000
Senior Unsecured Convertible Debt Issued on July 3, 2017 [Member] |  |  |
Net Investment Income [Line Items] |  |  |
Interest expense | $ 36,000,000 | 39,000,000 | 38,000,000
Issued date of senior unsecured convertible bonds | Jul. 03, 2017 |  |
Senior Unsecured Convertible Debt Issued on August 4, 2020 [Member] |  |  |
Net Investment Income [Line Items] |  |  |
Interest expense | $ 9,000,000 |  |
Issued date of senior unsecured convertible bonds | Aug. 04, 2020 |  |
Senior Unsecured Convertible Debt [Member] |  |  |
Net Investment Income [Line Items] |  |  |
Non-cash interest expense accretion of discount on liability component | $ 42,000,000 | $ 37,000,000 | $ 36,000,000

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