Retirement And Employee Benefit Plans (Narrative) (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
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan included in accumulated other comprehensive income (loss), before tax			$ (31)	$ (42)
Defined benefit plan included in accumulated other comprehensive income (loss), after tax			(19)	(25)
Classified to accumulated other comprehensive income (loss)			6	$ (1)	$ (15)
Expected future net loss			(1)
Company's expected additional annual contribution			$ 15
Common Stock in Treasury, Shares			31,269	47,149
401 (k) Defined Contribution Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Contribution expense			$ 4	$ 3	3
Contributions capitalized			2	4	3
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Non-cash curtailment gain (loss)	$ (1)		(1)
Settlement loss			(11)
Lump-sum payment			37
Net periodic benefit cost (gain)			24	15	12
Change in accumulated other comprehensive income (loss)			7	(2)
Change in accumulated other comprehensive income (loss) after tax			4	(2)
Employer contributions			10	12
Benefit obligation			$ 117	$ 138	134
Discount rate			4.20%	4.60%
Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Non-cash curtailment gain (loss)		$ 6	$ 6
Settlement loss
Net periodic benefit cost (gain)			(3)	4	3
Change in accumulated other comprehensive income (loss)			3	1
Change in accumulated other comprehensive income (loss) after tax			2	1
Employer contributions			1
Benefit obligation			$ 13	$ 20	$ 18
Discount rate			4.20%	4.60%