Retirement and Employee Benefit Plans (Amounts Recognized in Other Comprehensive Income) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Net actuarial (loss) gain arising during the year	$ (11)	$ (13)
Amortization of prior service cost
Amortization of net loss	2	20
Settlements
Tax effect	3	(3)
Total	(6)	4
Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Net actuarial (loss) gain arising during the year	(2)	2
Amortization of prior service cost
Amortization of net loss
Settlements		1
Tax effect	1	(1)
Total	$ (1)	$ 2