Employee Benefit Plans - Accumulated Other Comprehensive Income and Net Periodic Benefit Cost (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Postretirement Medical Plan
Accumulated Other Comprehensive (Income) Loss, Defined Benefit Plan, after Tax [Abstract]
Actuarial (loss) gain	$ (2)	$ (12)
AOCI	(2)	(12)
Net periodic benefit (income) expense:
Service cost - benefits earned during the year	0	1	$ 0
Interest cost	1	1	2
Amortization of actuarial gain	(2)	(1)	0
Net periodic benefit income	$ (1)	$ 1	$ 2
Defined Benefit Plan, Assumptions Used in Calculations [Abstract]
Discount rate - net periodic benefit costs			3.90%
Discount rate - benefit obligations	3.09%	4.21%
Minimum | Postretirement Medical Plan
Defined Benefit Plan, Assumptions Used in Calculations [Abstract]
Discount rate - net periodic benefit costs	3.87%	3.11%
Maximum | Postretirement Medical Plan
Defined Benefit Plan, Assumptions Used in Calculations [Abstract]
Discount rate - net periodic benefit costs	4.36%	3.67%
United States
Accumulated Other Comprehensive (Income) Loss, Defined Benefit Plan, after Tax [Abstract]
Actuarial (loss) gain	$ (5)	$ (53)
Prior-service credit	0	0
AOCI	(5)	(53)
Net periodic benefit (income) expense:
Interest cost	66	59	$ 77
Expected return on plan assets	(90)	(92)	(93)
Amortization of prior-service credit	0	0	0
Recognized AOCI loss due to settlements	0	0	(1)
Net periodic benefit income	(24)	(33)	(17)
Amounts recognized in Other comprehensive income (loss)
Actuarial (gain) loss	(49)	58	(41)
Prior-service cost	0	0	0
Reclassification of recognized AOCI gain due to settlements	0	0	1
Reclassification of prior-service credit to net periodic benefit income	0	0	0
(Gain) loss recognized in Other comprehensive income (loss)	(49)	58	(40)
U.K. Plan
Accumulated Other Comprehensive (Income) Loss, Defined Benefit Plan, after Tax [Abstract]
Actuarial (loss) gain	(54)	5
Prior-service credit	18	19
AOCI	(36)	24
Net periodic benefit (income) expense:
Interest cost	29	28	34
Expected return on plan assets	(58)	(67)	(60)
Amortization of prior-service credit	(1)	(2)	(1)
Recognized AOCI loss due to settlements	0	0	0
Net periodic benefit income	(30)	(41)	(27)
Amounts recognized in Other comprehensive income (loss)
Actuarial (gain) loss	57	40	(72)
Prior-service cost	0	19	0
Reclassification of recognized AOCI gain due to settlements	0	0	0
Reclassification of prior-service credit to net periodic benefit income	1	2	1
(Gain) loss recognized in Other comprehensive income (loss)	$ 58	$ 61	$ (71)
Defined Benefit Plan, Assumptions Used in Calculations [Abstract]
Discount rate - net periodic benefit costs	2.56%	2.21%	2.70%
Discount rate - benefit obligations	2.04%	2.85%	2.53%
Expected long-term rate of return on plan assets	4.85%	4.95%	5.00%
Qualified Plan | United States
Defined Benefit Plan, Assumptions Used in Calculations [Abstract]
Discount rate - net periodic benefit costs	4.08%
Discount rate - benefit obligations	3.35%
Expected long-term rate of return on plan assets	5.80%
Qualified Plan | United States | Minimum
Defined Benefit Plan, Assumptions Used in Calculations [Abstract]
Discount rate - net periodic benefit costs		3.14%	3.83%
Discount rate - benefit obligations		4.18%	3.55%
Expected long-term rate of return on plan assets		3.00%	2.35%
Qualified Plan | United States | Maximum
Defined Benefit Plan, Assumptions Used in Calculations [Abstract]
Discount rate - net periodic benefit costs		3.38%	4.35%
Discount rate - benefit obligations		4.39%	3.71%
Expected long-term rate of return on plan assets		5.40%	5.65%
Nonqualified Plan | United States
Defined Benefit Plan, Assumptions Used in Calculations [Abstract]
Discount rate - net periodic benefit costs			4.35%
Nonqualified Plan | United States | Minimum
Defined Benefit Plan, Assumptions Used in Calculations [Abstract]
Discount rate - net periodic benefit costs	3.65%	2.84%
Discount rate - benefit obligations	2.72%	3.93%	3.21%
Nonqualified Plan | United States | Maximum
Defined Benefit Plan, Assumptions Used in Calculations [Abstract]
Discount rate - net periodic benefit costs	3.95%	3.21%
Discount rate - benefit obligations	3.20%	4.28%	3.60%