Retirement and Employee Benefit Plans (Amounts Recognized in Other Comprehensive Income) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	[1]
Defined Benefit Plan Disclosure [Line Items]
Total change in value of pension and postretirement liabilities	$ (5)	$ 3	$ 8
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Net actuarial (loss) gain arising during the year	(12)	(5)
Amortization of prior service cost	0	0
Amortization of net loss	1	2
Settlements	0	8
Curtailments	3	0
Tax effect	3	(1)
Total change in value of pension and postretirement liabilities	(5)	4
Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Net actuarial (loss) gain arising during the year	2	(1)
Amortization of prior service cost	0	0
Amortization of net loss	0	0
Settlements	0	0
Curtailments	0	0
Tax effect	(1)	0
Total change in value of pension and postretirement liabilities	$ 1	$ (1)

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