Leases - Schedule of Lease Expense (Details) $ in Millions	12 Months Ended
	Dec. 31, 2019 USD ($)
Leases [Abstract]
Operating lease expense	$ 2,558
Financing lease expense:
Amortization of right-of-use assets	523
Interest on lease liabilities	82
Total financing lease expense	605
Variable lease expense	243
Total lease expense	$ 3,406