Acquisitions And Divestitures (Narrative) (Detail) - USD ($) shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Business Acquisition [Line Items]
(Gain) loss on disposition of assets, net	$ (13)	$ 1	$ (667)	$ (109)
Funds held in escrow	0		0		$ 43
Common stock issued in business combination			291	$ 231
Northern Delaware Basin [Member]
Business Acquisition [Line Items]
Total cash consideration paid for acquisition			$ 160
Funds held in escrow					$ 43
Common stock issued in business combination (Shares)			2.2
Common stock issued in business combination			$ 291
Alpha Crude Connector [Member]
Business Acquisition [Line Items]
Proceeds From Sale Of Oil And Gas Property And Equipment			801
(Gain) loss on disposition of assets, net			655
Total equity method investment	129		129
Midland Basin [Member]
Business Acquisition [Line Items]
Total cash consideration paid for acquisition			595
VIE Assets	607		607
VIE Liabilities	$ 605		$ 605