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Income Taxes - Unrecognized Tax Benefits (Details) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Unrecognized tax benefits roll forward      
Gross unrecognized tax benefits at beginning of period $ (20) $ (20) $ (13)
Increases in tax positions for current year 0 0 (9)
Lapse in statute of limitations 0 0 2
Gross unrecognized tax benefits at end of period $ (20) $ (20) $ (20)