Incentive Plans (Narrative) (Details) (USD $)	12 Months Ended					12 Months Ended																		12 Months Ended										1 Months Ended		12 Months Ended								12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011 years	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2008	Dec. 31, 2011 Postretirement Benefit Obligations [Member]	Dec. 31, 2010 Postretirement Benefit Obligations [Member]	Dec. 31, 2009 Postretirement Benefit Obligations [Member]	Dec. 31, 2011 Declining Annually Until 2015 [Member]	Dec. 31, 2011 Declining Annually Until 2025 [Member]	Dec. 31, 2010 Series B [Member] Sendero [Member] employees	Dec. 31, 2011 Stock Option [Member]	Dec. 31, 2010 Stock Option [Member]	Dec. 31, 2009 Stock Option [Member]	Dec. 31, 2011 Performance Unit Awards [Member]	Dec. 31, 2010 Performance Unit Awards [Member]	Dec. 31, 2009 Performance Unit Awards [Member]	Dec. 31, 2011 ESPP [Member]	Dec. 31, 2011 Restricted Stock Equity Awards [Member]	Dec. 31, 2010 Restricted Stock Equity Awards [Member]	Dec. 31, 2009 Restricted Stock Equity Awards [Member]	Dec. 31, 2011 Restricted Stock Equity Awards [Member] Liability Awards [Member]	Dec. 31, 2010 Restricted Stock Equity Awards [Member] Liability Awards [Member]	Dec. 31, 2011 Phantom Unit Awards [Member]	Dec. 31, 2010 Phantom Unit Awards [Member]	Dec. 31, 2011 401 (K) Plan [Member] years	Dec. 31, 2010 401 (K) Plan [Member]	Dec. 31, 2009 401 (K) Plan [Member]	Dec. 31, 2011 Deferred Compensation Retirement Plan [Member]	Dec. 31, 2010 Deferred Compensation Retirement Plan [Member]	Dec. 31, 2009 Deferred Compensation Retirement Plan [Member]	Dec. 31, 2011 Compensation Costs [Member]	Dec. 31, 2011 Restricted Stock Equity Awards [Member]	May 31, 2010 Pioneer Southwest LTIP [Member]	May 31, 2008 Pioneer Southwest LTIP [Member]	Dec. 31, 2011 Pioneer Southwest LTIP [Member] years	Dec. 31, 2010 Pioneer Southwest LTIP [Member]	Dec. 31, 2009 Pioneer Southwest LTIP [Member]	Dec. 31, 2011 Pioneer Southwest LTIP [Member] Restricted Stock Equity Awards [Member]	Dec. 31, 2010 Pioneer Southwest LTIP [Member] Restricted Stock Equity Awards [Member]	Dec. 31, 2009 Pioneer Southwest LTIP [Member] Restricted Stock Equity Awards [Member]	Dec. 31, 2011 Pioneer Southwest LTIP [Member] Phantom Unit Awards [Member]	Dec. 31, 2011 Pioneer Long-Term Incentive Plan [Member]	Dec. 31, 2011 Performance Unit Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Each officer and key employee allowed contribution percent, base salary																													25.00%
Each officer and key employee allowed contribution percent, annual bonus																													100.00%
Matching contribution percentage																													100.00%
Officer's contribution limit for matching contribution																													10.00%
Key employee's contribution limit for matching contribution																													8.00%
Matching contributions																													$ 2,200,000	$ 1,900,000	$ 1,700,000
Participants annual salary contributions to 401(k) Plan, percentage																										80.00%
Matching contributions percent																										200.00%
Participants contribution limit for matching contribution, percentage																										5.00%
Matching contributions vesting period in years																										4
Compensation expense recognized as a result of matching contributions																										18,300,000	13,400,000	11,800,000
Unrecognized share-based compensation expense																																69,500,000
Unvested share and unit based compensation plans, including attributable to Liability Awards																																19,700,000
Remaining weighted average period for unvested share-based compensation plan awards		3
Stock-based compensation for all plans		(41,673,000)	(40,185,000)	(38,564,000)
Restricted shares or units as compensation to directors																																	645,471
Shares or units representing Liability Awards																																	202,411
Number of unvested shares																																	533,125
Fair value of shares for which restrictions lapsed															44,700,000	27,400,000	4,800,000		98,600,000	42,900,000	11,700,000
Amount of liabilities attributable to liability awards included in accounts payable																						9,200,000	4,900,000
Fair value of shares-restrictions lapsed																						6,700,000
Approved and authorized awards																																				3,000,000							9,100,000
Fair value assumptions, method used		Black-Sholes option-pricing model
Option awards contract life		10
Average dividend yield		7
Weighted average grant-date fair value												$ 49.61	$ 23.79	$ 6.27					$ 97.52	$ 48.32	$ 15.47																		$ 29.35	$ 22.87	$ 18.26
Intrinsic value of options exercised												1,500,000	6,900,000	3,100,000
Aggregate grant date fair values of the outstanding performance unit awards, per unit															$ 134.68	$ 63.52	$ 15.29
Long term incentive plan number of units limit																																			3,000,000
Restricted units to directors																																				6,812	8,744	12,909
Restricted units vested																																		10,871			2,038
Schedule over which restricted units vest (years)																																				3
Lapse of restrictions																																							342,000	324,000	145,000
Number of key employees participated in restricted unit agreements											2
Number of Units granted											1,000																															30,039		43,495	[1]
Grant date fair value											5,100,000
Service period for the performance unit awards, years																																												34-month
Employee stock purchase plan length of contribution term		eight-month offering period (January 1 to August 31)
Employee stock purchase plan contribution limit		15.00%
Employee stock purchase plan participants purchase price percent																		15.00%
Unfunded accumulated postretirement benefit obligations determined by actuaries		7,456,000	7,408,000	9,075,000	9,612,000	7,500,000	7,400,000
Number of plans reviewed by actuaries						4
Unfunded accumulated postretirement benefit obligations by actuaries						4,600,000
Number of plans reviewed by company						1
Unfunded accumulated postretirement benefit obligations determined by the Company						2,900,000
Discount rate to value benefit obligations						4.00%	4.00%	5.00%
Annual medical cost percentage escalation trends due current		8.00%
Annual medical cost percentage escalation trends due in five years and thereafter									7.00%	5.00%
Estimated benefit payments for 2012	854,000	854,000
Estimated interest costs for 2012	$ 596,000
Weighted Average Grant-Date Fair Value, Shares granted																								$ 32.16	$ 22.74																	$ 32.16		$ 134.68

[1] These amounts reflect the number of performance units granted. The actual payout of shares may be between zero percent and 250 percent of the performance units granted depending upon the total shareholder return ranking of the Company compared to peer companies at the vesting date.