Leases - Lease Cost and Additional Information (Details) $ in Millions	3 Months Ended	9 Months Ended
	Sep. 30, 2019 USD ($)	Sep. 30, 2019 USD ($)
Lessee, Lease, Description [Line Items]
Operating lease cost	$ 94	$ 276
Short-term lease cost	4	7
Variable lease cost	37	113
Sublease income	(4)	(12)
Net lease cost	$ 131	384
Operating cash outflows from operating leases		288
Right of use assets obtained in exchange for new operating lease liabilities		$ 112
Real Estate Lease
Lessee, Lease, Description [Line Items]
Weighted-average remaining lease term	8 years 10 months 9 days	8 years 10 months 9 days
Weighted-average discount rate	3.09%	3.09%