Long-Term Debt and Credit Facilities - Interest Expense (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Debt Disclosure [Abstract]
Gross interest expense	$ 2,230	$ 1,559	$ 1,372
Capitalized interest	(53)	(78)	(54)
Total interest expense	$ 2,177	$ 1,481	$ 1,318