Leases - Summary of the Components of Net Lease Cost (Details) $ in Millions	12 Months Ended
	Dec. 31, 2019 USD ($)
Leases [Abstract]
Operating lease cost	$ 2,720
Finance lease cost:
Amortization of right-of-use assets	38
Interest on lease liabilities	44
Total finance lease costs	82
Short-term lease costs	24
Variable lease costs	581
Less: sublease income	50
Net lease cost	$ 3,357