Employee Benefit Plans - Benefit Obligations and Funded Status for Medical Plan (Details) - Postretirement Medical Plan - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Projected benefit obligation at beginning of year	$ 34	$ 40
Service cost - benefits earned during the year	0	1	$ 0
Interest cost on projected benefit obligation	1	1	2
Actuarial loss (gain)	(9)	5
Participant contributions	1	2
Benefits paid	(4)	(4)
Projected benefit obligation at end of year	41	34	$ 40
Funded status of the plan	(41)	(34)
Amounts recognized in the balance sheet consist of:
Current liabilities	(3)	(3)
Long-term liabilities	(38)	(31)
Net amount recognized	$ (41)	$ (34)
Discount rate assumption as of December 31	3.09%	4.21%