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Stock-Based Compensation (Performance Share Awards Compensation Expense) (Details) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Compensation Expense Recorded [Line Items]      
Compensation expense $ 71 $ 64 $ 58
Performance Share Awards      
Compensation Expense Recorded [Line Items]      
Compensation expense 60 53 47
Cash settlements 19 13 15
Stock settlements $ 79 $ 39 $ 66