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Income Taxes - Summary of Valuation Allowance (Details) - Valuation Allowance of Deferred Tax Assets [Member] - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Movement in Valuation Allowances and Reserves [Roll Forward]      
Balance at January 1, $ 10 $ 2 $ 17
Net charges to income tax expense 14 8 0
Release of valuation allowance 0 0 (15)
Balance at December 31, $ 24 $ 10 $ 2