Leases - Information Related to Operating Leases (Details) $ in Millions	3 Months Ended	6 Months Ended
	Jun. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)
Leases [Abstract]
Right-of-use assets	$ 8,118	$ 8,118
Lease liabilities	$ 8,404	$ 8,404
Weighted average remaining lease term (in years)	8 years 8 months 12 days	8 years 8 months 12 days
Weighted average discount rate	3.75%	3.75%
Supplemental cash flow information
Cash paid for amounts included in the measurement of lease liabilities - operating cash flows		$ 778
Supplemental non-cash information
Right-of-use assets obtained in exchange for operating lease obligations		587
Rental expense
Gross rental expense	$ 506	1,020
Sublease rental income	(42)	(88)
Net rental expense	$ 464	$ 932