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Leases - Narrative (Details) - USD ($)
$ in Millions
3 Months Ended 9 Months Ended
Sep. 30, 2018
Sep. 30, 2018
Sep. 30, 2019
Leases [Abstract]      
Operating lease expense $ 184 $ 558  
Lessee, Lease, Description [Line Items]      
Operating lease, weighted-average remaining lease term     8 years
Operating lease, weighted-average discount rate     4.30%
All other assets      
Lessee, Lease, Description [Line Items]      
Operating lease assets     $ 809