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Income Taxes Accounting for Uncertainty in Income Taxes (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2020
Income Tax Disclosure [Abstract]        
Unrecognized Tax Benefits $ 20 $ 20 $ 20 $ 19
Unrecognized Tax Benefits that Would Impact Effective Tax Rate       17
Significant Change in Unrecognized Tax Benefits is Reasonably Possible, Amount of Unrecorded Benefit       $ 2
Increase (Decrease) in Interest Accrued for Unrecognized Tax Benefits     1  
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns        
Unrecognized Tax Benefits, Beginning of Period 20 20 22  
Reduction due to lapse of statute of limitations (1) (1) (2)  
Unrecognized Tax Benefits, Increase Resulting from Prior Period Tax Positions   1    
Unrecognized Tax Benefits, End of Period $ 19 $ 20 $ 20