Retirement and Employee Benefit Plans (Pension and Other Postretirement Benefit Costs) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Defined Benefit Plan Disclosure [Line Items]
Curtailment gain			$ (4)
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 7	$ 7	10
Interest cost	5	5	5
Expected return on plan assets	(6)	(6)	(7)
Amortization of transition obligation	0	0	0
Amortization of prior service cost	0	0	0
Amortization of net loss	1	2	2
Net periodic benefit cost	7	8	10
Curtailment gain	0	0	0
Settlement loss	0	6	0
Total benefit cost (benefit)	7	14	10
Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	2	1	2
Interest cost	0	0	1
Expected return on plan assets	0	0	0
Amortization of transition obligation	0	0	0
Amortization of prior service cost	0	0	0
Amortization of net loss	0	0	0
Net periodic benefit cost	2	1	3
Curtailment gain	0	0	(4)
Settlement loss	0	0	0
Total benefit cost (benefit)	$ 2	$ 1	$ (1)