Retirement And Employee Benefit Plans (Pension And Other Postretirement Benefit Costs) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 16	$ 13	$ 14
Interest cost	6	5	4
Expected return on plan assets	$ (9)	$ (7)	$ (6)
Amortization of transition obligation
Amortization of prior service cost
Amortization of net loss	$ 2	$ 1	$ 2
Net periodic benefit cost	15	12	14
Total benefit cost	15	12	14
Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	3	2	2
Interest cost	$ 1	$ 1	$ 1
Amortization of transition obligation
Amortization of prior service cost
Net periodic benefit cost	$ 4	$ 3	$ 3
Total benefit cost	$ 4	$ 3	$ 3