Employee Benefit Obligations - Total (Details) - USD ($) $ in Millions	Jun. 30, 2019	Dec. 31, 2018
Employee Benefit Obligations
Underfunded defined benefit pension liabilities	$ 920	$ 954
Less current portion	(25)	(25)
Long-term defined benefit pension liabilities	895	929
Long-term retiree medical liabilities	159	157
Deferred compensation plans	372	291
Other	39	78
Total non-current employee benefit obligations	$ 1,465	$ 1,455