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Income Taxes - Deferred Tax Assets and Valuation Allowances (Details) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Valuation Allowance [Line Items]    
Net operating loss carryforwards $ 1,484 $ 1,261
Tax credit carryforwards 257 258
Valuation allowance related to deferred tax assets 138 155
Change in valuation allowances (17)  
Net Operating Loss Carryovers Tax Credits and Capital Losses    
Valuation Allowance [Line Items]    
Valuation allowance related to deferred tax assets 100 $ 117
Operating Loss Carryforward | State and Local Jurisdiction    
Valuation Allowance [Line Items]    
Change in valuation allowances (9)  
Operating Loss Carryforward | Foreign Tax Authority    
Valuation Allowance [Line Items]    
Change in valuation allowances $ (8)