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Revenue Recognition Accounting Policy (Details 3) - USD ($)
$ in Millions
3 Months Ended 6 Months Ended
Jun. 30, 2019
Jun. 30, 2018
Jun. 30, 2019
Jun. 30, 2018
Dec. 31, 2018
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]          
Total Revenues $ 1,310 $ 1,368 $ 2,564 $ 2,739  
Deferred Revenue $ 419   419   $ 414
Deferred Revenue, Revenue Recognized     (33)    
Deferred Revenue, Additions     $ 38