Retirement And Employee Benefit Plans (Changes In The Plans Benefit Obligations, Fair Value Of Assets, And Funded Status) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Pension Benefits [Member]
Change in benefit obligations:
Benefit obligation at January 1	$ 138	$ 134
Service cost	11	16	$ 13
Interest cost	5	6	5
Participant contributions
Actuarial loss (gain)	14	(7)
Benefits paid	(3)	(11)
Plan amendments
Curtailments	(8)
Settlements	(40)
Benefit obligation at December 31	117	138	134
Change in plan assets:
Fair value of plan assets at January 1	108	108
Actual return on plan assets	3	(1)
Employer contributions	10	12
Participant contributions
Benefits paid	(3)	(11)
Settlements	(37)
Fair value of plan assets at December 31	81	108	108
Funded status of plans at December 31	(36)	(30)
Other Postretirement Benefits [Member]
Change in benefit obligations:
Benefit obligation at January 1	20	18
Service cost	2	3	2
Interest cost	1	1	1
Participant contributions
Actuarial loss (gain)	(2)	(2)
Benefits paid	(1)
Plan amendments
Curtailments	(7)
Settlements
Benefit obligation at December 31	13	20	18
Change in plan assets:
Fair value of plan assets at January 1
Actual return on plan assets
Employer contributions	1
Participant contributions
Benefits paid	(1)
Settlements
Fair value of plan assets at December 31
Funded status of plans at December 31	$ (13)	$ (20)