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Pension and Other Postretirement Benefits (Schedule of One-Percentage-Point Change in Assumed Health Care Cost Trend Rates) (Details) - Other Postretirement Benefits
$ in Millions
12 Months Ended
Dec. 31, 2018
USD ($)
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]  
Effect on total service and interest cost, Increase $ 1
Effect on total service and interest cost, Decrease 1
Effect on postretirement benefit obligation, Increase 8
Effect on postretirement benefit obligation, Decrease $ 7