Summary Of Significant Accounting Policies (Narrative) (Details)	12 Months Ended
	Dec. 31, 2018 USD ($) Customer	Dec. 31, 2017 USD ($) Customer	Dec. 31, 2016 USD ($) Customer
Summary Of Significant Accounting Policies [Line Items]
Concentration risk percentage | Customer	1	0	0
Derivative collateral held	$ 0
Cash collateral posted	0
ASU 2017-07 [Member]
Summary Of Significant Accounting Policies [Line Items]
Reclassification of non-service cost components of net periodic benefit costs		$ 7,000,000	$ 14,000,000
ASU 2018-02 [Member]
Summary Of Significant Accounting Policies [Line Items]
Cumulative effect on retained earnings	33,000,000
ASU 2016-02 [Member] | Scenario Plan [Member]
Summary Of Significant Accounting Policies [Line Items]
Cumulative effect on retained earnings	(19,000,000)
Right-of-use assets expects to recognize	400,000,000
Cumulative effect on retained earnings, before tax	$ (24,000,000)
Minimum [Member]
Summary Of Significant Accounting Policies [Line Items]
Other property and equipment, useful life	3 years
Maximum [Member]
Summary Of Significant Accounting Policies [Line Items]
Other property and equipment, useful life	60 years
Customer Concentration Risk [Member] | One Customer [Member] | Consolidated Sales Revenue [Member]
Summary Of Significant Accounting Policies [Line Items]
Concentration risk percentage	11.00%
Upstream Revenues [Member]
Summary Of Significant Accounting Policies [Line Items]
Number of days allowed for payment from end of production month	30 days
Marketing Revenues [Member]
Summary Of Significant Accounting Policies [Line Items]
Number of days allowed for payment of invoiced amount	30 days