Summary Of Significant Accounting Policies (Changes of Ownership Interest) (Details) (USD $) Share data in Millions, unless otherwise specified	0 Months Ended	12 Months Ended
	Dec. 12, 2011	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Nov. 16, 2009
Net Income (loss) attributable to common stockholders		$ 834,489,000	$ 605,208,000	$ (52,106,000)
Net income (loss) attributable to common stockholders and transfers from noncontrolling interest		869,508,000		(18,718,000)
Issued Common Units	4.4
Sale of Common Units		1.8
Pioneer Southwest [Member]
Net Income (loss) attributable to common stockholders			605,208,000
Increase in additional paid in capital		48,792,000
Increase in additional paid in capital for the sale of 1.8 million Pioneer Southwest common units on December 12, 2011, net of tax of $15.4 million		35,091,000
Net transfers from noncontrolling interest		35,019,000		33,388,000
Net income (loss) attributable to common stockholders and transfers from noncontrolling interest			605,208,000
Issued Common Units	2.6	2.6			3.1
Units Issued, Tax	23,700,000
Sale of Common Units	1.8
Sale of Units, Tax	15,400,000
Additional Paid-In Capital [Member]
Increase in additional paid in capital		8,104,000
Additional Paid-In Capital [Member] | Pioneer Southwest [Member]
Increase in additional paid in capital		8,104,000		33,388,000
Increase in additional paid in capital for the sale of 1.8 million Pioneer Southwest common units on December 12, 2011, net of tax of $15.4 million		$ 26,915,000