Employee Benefit Obligations - Total (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Employee Benefit Obligations
Underfunded defined benefit pension liabilities	$ 718	$ 955
Less current portion	(22)	(24)
Long-term defined benefit pension liabilities	696	931
Long-term retiree medical liabilities	148	156
Deferred compensation plans	417	439
Other	61	87
Total non-current employee benefit obligations	$ 1,322	$ 1,613