Leases - Operating and Finance Lease Liability Reconciliation (Details) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Leases [Abstract]
Gross lease liabilities - operating leases	$ 30,550
Gross lease liabilities - finance leases	27,310
Gross lease liabilities	57,860
Imputed interest - operating leases	(6,646)
Imputed interest - finance leases	(1,936)
Imputed interest	(8,582)
Present value of operating leases	23,904
Present value of finance leases	25,374
Present value of lease liabilities	49,278
Current portion of operating lease liabilities	(2,842)
Current portion of finance lease liabilities	(9,378)
Current portion of lease liabilities	(12,220)
Total long-term operating lease liabilities	21,062
Total long-term finance lease liabilities	15,996
Total long-term lease liabilities	$ 37,058	$ 9,650