Leases - Operating and Finance Lease Liability Reconciliation (Details) - USD ($) $ in Millions	Jun. 30, 2019	Dec. 31, 2018
Leases [Abstract]
Gross lease liabilities - operating leases	$ 28,739
Gross lease liabilities - finance leases	26,204
Gross lease liabilities	54,943
Imputed interest - operating leases	(6,324)
Imputed interest - finance leases	(1,970)
Imputed interest	(8,294)
Present value of operating leases	22,415
Present value of finance leases	24,234
Present value of lease liabilities	46,649
Current portion of operating lease liabilities	(2,631)
Current portion of finance lease liabilities	(8,884)
Current portion of lease liabilities	(11,515)
Total long-term operating lease liabilities	19,784
Total long-term finance lease liabilities	15,350
Total long-term lease liabilities	$ 35,134	$ 9,650