Other Long-Term Liabilities - Long Term Finance Lease Obligation (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Other Liabilities Disclosure [Abstract]
Gross finance lease obligations	$ 6,265
Less imputed interest	(1,238)
Present value of net minimum lease payments	5,027
Less current portion of finance lease obligations	(282)	$ (144)
Total long-term finance lease obligations	$ 4,745	$ 2,439