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Revenue (Narratives) (Details) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Revenue from Contract with Customer [Abstract]      
Remaining revenue recognition $ 762 $ 740 $ 741
Remaining revenue recognition $ 20,500    
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2020-01-01      
Revenue from Contract with Customer [Abstract]      
Remaining performance obligation, percentage 35.00%    
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]      
Performance obligations expected to be satisfied, expected timing 12 months    
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2021-01-01      
Revenue from Contract with Customer [Abstract]      
Remaining performance obligation, percentage 25.00%    
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]      
Performance obligations expected to be satisfied, expected timing 24 months