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Significant Accounting Policies - Adoption of ASC 842 on Unaudited Condensed Consolidated Balance Sheet (Parenthetical) (Details) - USD ($)
$ in Millions
12 Months Ended
Jan. 01, 2019
Dec. 31, 2019
Dec. 31, 2018
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]      
Recorded a net increase in opening retained earnings   $ 3 $ 4
Accounting Standards Update 2016-02 | Adjustments Due to ASC 842      
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]      
Recorded a net increase in opening retained earnings $ 3