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Share-Based Compensation (Summary of Unrecognized Compensation Cost And Weighted Average Period For Recognition) (Details)
$ in Millions
6 Months Ended
Jun. 30, 2021
USD ($)
Restricted Stock Awards [Member]  
Unrecognized Compensation And Weighted Average Recognition [Line Items]  
Unrecognized compensation cost $ 111
Weighted average period for recognition (years) 2 years 7 months 6 days
Performance Share Units [Member]  
Unrecognized Compensation And Weighted Average Recognition [Line Items]  
Unrecognized compensation cost $ 18
Weighted average period for recognition (years) 2 years 1 month 6 days