Summary Of Significant Accounting Policies (Changes of Ownership Interest) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Net Income (loss) attributable to common stockholders	$ 930	$ (838)	$ 192
Deferred tax provision attributable to 2008 Pioneer Southwest initial public offering	0	0	(49)
Pioneer Southwest noncontrolling interest transferred to APIC		0
Deferred tax benefit associated with the Pioneer Southwest merger	0	200	0
Pioneer Southwest merger transaction costs	(1)	(4)
Net transfers from noncontrolling interest	(1)	365	(49)
Net income (loss) attributable to common stockholders and transfers from noncontrolling interest	929	(473)	143
Additional Paid-In Capital [Member]
Deferred tax provision attributable to 2008 Pioneer Southwest initial public offering			(49)
Pioneer Southwest noncontrolling interest transferred to APIC		169
Deferred tax benefit associated with the Pioneer Southwest merger		200
Pioneer Southwest merger transaction costs	(1)	(4)
Additional Paid-In Capital [Member] | Pioneer Southwest [Member]
Deferred tax provision attributable to 2008 Pioneer Southwest initial public offering	0	0	(49)
Pioneer Southwest noncontrolling interest transferred to APIC	0	169	0
Deferred tax benefit associated with the Pioneer Southwest merger	0	200	0
Pioneer Southwest merger transaction costs	$ (1)	$ (4)	$ 0