Leases - Operating and Finance Lease Liability Reconciliation (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Leases [Abstract]
Gross lease liabilities - operating leases	$ 26,731
Gross lease liabilities - finance leases	25,004
Gross lease liabilities	51,735
Imputed interest - operating leases	(5,850)
Imputed interest - finance leases	(1,810)
Imputed interest	(7,660)
Present value of operating leases	20,881
Present value of finance leases	23,194
Present value of lease liabilities	44,075
Current portion of operating lease liabilities	(2,490)
Current portion of finance lease liabilities	(8,310)
Current portion of lease liabilities	(10,800)
Total long-term operating lease liabilities	18,391
Total long-term finance lease liabilities	14,884
Total long-term lease liabilities	$ 33,275	$ 9,650