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Pension and Other Postretirement Benefit Plans (Estimated Impact of One Percentage-Point Change in Assumed Health Care Cost Trend Rate) (Details)
$ in Millions
12 Months Ended
Dec. 31, 2019
USD ($)
Defined Benefit Plan [Abstract]  
Effect on total of service and interest cost, one percentage point increase $ 0
Effect on total of service and interest cost, one percentage point decrease 0
Effect on postretirement benefit obligations, one percentage point increase 3
Effect on postretirement benefit obligations, one percentage point decrease $ (2)