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Leases (Narrative) (Details) - USD ($)
$ in Millions
Dec. 31, 2019
Dec. 31, 2018
Operating Leased Assets [Line Items]    
Operating Lease, Right-of-Use Asset $ 971  
Operating Lease, Liability, Current 215 $ 0
Operating Lease, Liability, Noncurrent $ 781  
Minimum [Member]    
Operating Leased Assets [Line Items]    
Lessee, Operating Lease, Renewal Term 1 month  
Maximum [Member]    
Operating Leased Assets [Line Items]    
Lessee, Operating Lease, Renewal Term 49 years