Leases - Information Related to Operating Leases (Details) $ in Millions	3 Months Ended	9 Months Ended
	Sep. 30, 2019 USD ($)	Sep. 30, 2019 USD ($)
Leases [Abstract]
Right-of-use assets	$ 8,160	$ 8,160
Lease liabilities	$ 8,425	$ 8,425
Weighted average remaining lease term (in years)	8 years 8 months 12 days	8 years 8 months 12 days
Weighted average discount rate	3.73%	3.73%
Supplemental cash flow information
Cash paid for amounts included in the measurement of lease liabilities - operating cash flows		$ 1,177
Supplemental non-cash information
Right-of-use assets obtained in exchange for operating lease obligations		990
Rental expense
Gross rental expense	$ 517	1,537
Sublease rental income	(49)	(137)
Net rental expense	$ 468	$ 1,400