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Revenue (Narrative) (Details) - USD ($)
$ in Millions
3 Months Ended 6 Months Ended
Jun. 30, 2020
Jun. 30, 2020
Dec. 31, 2019
Disaggregation of Revenue [Line Items]      
Lease transactions $ 9 $ 9 $ 9
Advanced billings, revenue recognized $ 75    
Expected timing of satisfaction period   12 months  
Business services | Minimum      
Disaggregation of Revenue [Line Items]      
Period of recognition   1 year  
Business services | Maximum      
Disaggregation of Revenue [Line Items]      
Period of recognition   5 years