Employee Benefit Obligations - Total (Details) - USD ($) $ in Millions	Sep. 30, 2017	Dec. 31, 2016
Employee Benefit Obligations
Underfunded defined benefit pension liabilities	$ 877	$ 963
Less current portion	(26)	(25)
Long-term defined benefit pension liabilities	851	938
Retiree medical and other postemployment benefits	213	226
Deferred compensation plans	279	272
Other	63	61
Total non-current employee benefit obligations	$ 1,406	$ 1,497