Employee Benefit Obligations - Total (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Employee Benefit Obligations
Underfunded defined benefit pension liabilities	$ 929	$ 918
Less current portion	(24)	(24)
Long-term defined benefit pension liabilities	905	894
Long-term retiree medical liabilities	164	156
Deferred compensation plans	333	362
Other	33	74
Total non-current employee benefit obligations	$ 1,435	$ 1,486