Leases - Operating Lease Portfolio and Related Lease Costs (Details) $ in Millions	3 Months Ended
	Mar. 31, 2019 USD ($)
Lessee, Lease, Description [Line Items]
Right-of-use assets	$ 1,547
Lease liabilities	$ 1,836
Weighted average remaining lease term	9 years 2 months 12 days
Weighted average discount rate	3.30%
Operating lease cost	$ 65
Variable lease cost	11
Total lease cost	76
Sublease income	(6)
Net lease cost	70
Cash paid for amounts included in the measurement of lease liabilities	82
Right-of-use assets obtained in exchange for lease liabilities	15
Accounting Standards Update 2016-02
Lessee, Lease, Description [Line Items]
Right-of-use assets	1,601
Lease liabilities	$ 1,900