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Employee Benefit Plans (Effects of a One-Percentage Point Increase and Decrease in Assumed Health Care Cost Trend Rates) (Details) - Other Postretirement Benefits
$ in Millions
12 Months Ended
Dec. 31, 2019
USD ($)
Defined Benefit Plan Disclosure [Line Items]  
Increase in total service and interest costs $ 6
Increase in postretirement benefit obligation 110
Decrease in total service and interest costs 5
Decrease in postretirement benefit obligation $ 102