Retirement and Employee Benefit Plans (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Defined Benefit Plan Disclosure [Line Items]
Defined contribution plan cost	$ 2	$ 2	$ 3
Contributions capitalized	1	1	2
Non-cash curtailment gain			4
Lump-sum payment		21
Defined benefit plan included in accumulated other comprehensive (income) loss, before tax	36	30
Defined benefit plan included in accumulated other comprehensive (income) loss after tax	28	22
Total change in value of pension and postretirement liabilities	5	(3)	(8)	[1]
Expected future net loss	1
Company's expected additional annual contribution	13
Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Non-cash curtailment gain	0	0	4
Settlement loss	0	0	0
Total change in value of pension and postretirement liabilities	(1)	1
Employer contributions	1	2
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Non-cash curtailment gain	0	0	0
Settlement loss	0	6	$ 0
Total change in value of pension and postretirement liabilities	5	(4)
Employer contributions	$ 12	$ 12

[1] In 2018, deferred tax activity incurred in other comprehensive income was offset by a valuation allowance.