Retirement And Employee Benefit Plans (Pension And Other Postretirement Benefit Costs) (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost			$ 11	$ 16	$ 13
Interest cost			5	6	5
Expected return on plan assets			(6)	(9)	(7)
Amortization of transition obligation
Amortization of prior service cost
Amortization of net loss			2	2	1
Net periodic benefit cost			12	15	12
Curtailment loss	$ 1		1
Settlement loss			11
Total benefit cost (benefit)			24	15	12
Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost			2	3	2
Interest cost			1	1	1
Expected return on plan assets
Amortization of transition obligation
Amortization of prior service cost
Amortization of net loss
Net periodic benefit cost			3	4	3
Curtailment loss		$ (6)	(6)
Settlement loss
Total benefit cost (benefit)			$ (3)	$ 4	$ 3