Leases - Lease Cost and Additional Information (Details) $ in Millions	3 Months Ended	6 Months Ended
	Jun. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)
Lessee, Lease, Description [Line Items]
Operating lease cost	$ 100	$ 182
Short-term lease cost	2	3
Variable lease cost	39	76
Sublease income	(4)	(8)
Net lease cost	$ 137	253
Operating cash outflows from operating leases		187
Right of use assets obtained in exchange for new operating lease liabilities		$ 67
Real Estate Lease
Lessee, Lease, Description [Line Items]
Weighted-average remaining lease term	8 years 11 months 26 days	8 years 11 months 26 days
Weighted-average discount rate	3.08%	3.08%