Fair Value Measurements (Reconciliation Of Net Beginning And Ending Balances Recorded For Net Assets And Liabilities Classified As Level 3) (Detail) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance		$ 342	$ 478	$ 625
Contingent consideration payment	[1]	(200)	(189)	(180)
Net derivative positions assumed - MarkWest Merger		0	31	0
Unrealized and realized losses included in net income		55	20	33
Settlements of derivative instruments		(7)	2	0
Ending balance		190	342	478
Contingent consideration payment		$ 164	$ 175	$ 172

[1] On the consolidated statements of cash flows for 2016, 2015 and 2014, $164 million, $175 million and $172 million, respectively, of the contingent earnout payment to BP was included as a financing activity with the remainder included as an operating activity.