Retirement and Employee Benefit Plans (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018		Dec. 31, 2017
Defined Benefit Plan Disclosure [Line Items]
Defined contribution plan cost	$ 2	$ 3		$ 3
Contributions capitalized	1	2		2
Non-cash curtailment gain (loss)		4
Lump-sum payment	21
Defined benefit plan included in accumulated other comprehensive (income) loss, before tax	30	34
Defined benefit plan included in accumulated other comprehensive (income) loss after tax	22	20
Change in value of pension and postretirement in AOCI	3	8	[1]	(11)	[1]
Expected future net loss	1
Company's expected additional annual contribution	13
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Non-cash curtailment gain (loss)	0	0		0
Settlement loss	6	0		0
Change in value of pension and postretirement in AOCI	4	4
Employer contributions	12	12
Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Non-cash curtailment gain (loss)	0	4		0
Settlement loss	0	0		$ 0
Change in value of pension and postretirement in AOCI	(1)	2
Employer contributions	$ 2	$ 1

[1] In 2018 and 2017, deferred tax activity incurred in other comprehensive income was offset by a valuation allowance.