Employee Benefit Plans (Details) (USD $)	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Stock based compensation by job function [Line Items]
Compensation expense related to the company's stock-based compensation plans	$ 128,205,000	$ 107,314,000	$ 95,037,000
Maximum shares of stock-based awards approved	12,900,000
Common Shares Available for Grant	5,400,000
Federal income tax (expense) / benefit recognized from stock-based compensation	25,000	(1,000,000)	76,000,000
Vesting schedule for stock options and SARs granted	four years
Maximum term of stock options and SARs granted (in years)	10
Percentage of the fair market value at which employees may purchase company stock via the ESPP	85
Maximum Percentage Of Employee Pay Eligible For Contribution To Espp Percentage	10.00%
Term Of Espp Offering Period Description	two six-month offering periods
Stock-based compensation expense related to stock options, SAR and ESPP grants	48,000,000	41,000,000	38,000,000
Summary Information By Grant Price Range For Stock Options And SARs Outstanding And Exercisable At End Of Period [Line Items]
Aggregate Intrinsic Value For Outstanding Options and SARs	241,474
Aggregate Intrinsic Value For Exercisable Units	203,646
Unrecognized compensation expense related to non-vested stock option and SAR grants	87,900,000
Weighted average period over which unrecognized compensation expense will be recognized (in years)	2.8
Share Based Compensation Arrangement By Share Based Payment Award ESPP [Abstract]
Stock Options/SARs Exercisable at December 31 (in shares)	5,148,000	5,439,000	5,394,000
Available for Future Grant (in shares)	5,400,000
Intrinsic value of stock options/SARs exercised during the period	78,400,000	66,000,000	21,400,000
Stock options/SARs vested or expected to vest (in shares)	8,123,226
Weighted average grant price for stock options/SARs vested or expected to vest (per share)	$ 69.48
Intrinsic value of stock options/SARs vested or expected to vest	238,500,000
Weighted average remaining contractual life of stock options/SARs vested or expected to vest (in years)	3.6
Employee Service Share Based Compensation Unrecognized Compensation Costs On Nonvested Restricted Stock Awards	132,600,000
Stock Options And Sars [Member]
Weighted Average Fair Value And Valuation Assumptions Used To Value ESPP Stock Based Compensation [Abstract]
Weighted Average Fair Value of Grants	$ 29.92	$ 32.12	$ 30.13
Expected Volatility (in hundredths)	40.96%	39.70%	41.90%
Risk-Free Interest Rate (in hundredths)	0.58%	0.87%	1.42%
Dividend Yield (in hundredths)	0.70%	0.70%	0.70%
Expected Life (in years)	5.6	5.5	5.5
Stock option and SAR Rollforward [Abstract]
Outstanding at January 1	8,445,000	8,335,000	7,802,000
Granted	1,509,000	1,450,000	1,270,000
Exercised (1)	(1,399,000)	(1,144,000)	(636,000)
Forfeited	(181,000)	(196,000)	(101,000)
Outstanding at December 31	8,374,000	8,445,000	8,335,000
Share Based Compensation Arrangement By Share Based Payment Award ESPP [Abstract]
Outstanding at January 1 - Price per Share	$ 64.49	$ 57.08	$ 52.56
Granted - Price Per Share	$ 85.29	$ 93.07	$ 80.95
Exercised - Price Per Share	$ 50.86	$ 43.38	$ 46.56
Forfeited - Price per Share	$ 87.74	$ 84.22	$ 74.07
Outstanding at December 31 - Price per Share	$ 70.01	$ 64.49	$ 57.08
Stock Options/SARs Exercisable at December 31 (price per share)	$ 59.19	$ 51.71	$ 44.45
Espp [Member]
Stock based compensation by job function [Line Items]
Common Shares Available for Grant	790,000
Weighted Average Fair Value And Valuation Assumptions Used To Value ESPP Stock Based Compensation [Abstract]
Weighted Average Fair Value of Grants	$ 22.75	$ 25.45	$ 25.78
Expected Volatility (in hundredths)	29.82%	38.30%	78.89%
Risk-Free Interest Rate (in hundredths)	0.14%	0.18%	0.25%
Dividend Yield (in hundredths)	0.70%	0.70%	1.00%
Expected Life (in years)	0.5	0.5	0.5
Share Based Compensation Arrangement By Share Based Payment Award ESPP [Abstract]
Available for Future Grant (in shares)	790,000
Approximate Number Of Participants In Espp	1,525	1,236	1,128
Employee Stock Purchase Plan Espp Shares Contributed To Espp	135,000	114,000	72,000
Employee Stock Purchase Plan Espp Cash Contributions To Espp	10,947,000	9,172,000	4,150,000
Restricted Stock And Restricted Stock Units [Member]
Stock option and SAR Rollforward [Abstract]
Outstanding at January 1	4,009,000	3,636,000	3,048,000
Granted	932,000	850,000	1,197,000
Exercised (1)	(457,000)	(364,000)	(553,000)
Forfeited	(244,000)	(113,000)	(56,000)
Outstanding at December 31	4,240,000	4,009,000	3,636,000
Share Based Compensation Arrangement By Share Based Payment Award ESPP [Abstract]
Outstanding at January 1 - Price per Share	$ 79.13	$ 73.69	$ 70.24
Granted - Price Per Share	$ 90.87	$ 93.39	$ 63.13
Exercised - Price Per Share	$ 66.10	$ 58.00	$ 31.35
Forfeited - Price per Share	$ 82.45	$ 79.37	$ 78.18
Outstanding at December 31 - Price per Share	$ 82.93	$ 79.13	$ 73.69
Share Based Compensation Restricted Stock Arrangement By Share Based Payment Award Award Vesting Period	five years
Share Based Compensation Arrangement By Restricted Stock And Restricted Stock Units Compensation Cost	80,000,000	66,000,000	57,000,000
Employee Service Share Based Compensation Unrecognized Compensation Costs On Nonvested Restricted Stock Awards Weighted Average Period Of Recognition	2.4
Intrinsic value of restricted stock and restricted stock units released during the year	$ 44,400,000	$ 35,200,000	$ 36,900,000
Aggregate Intrinsic Value Of Restricted Stock And Restricted Stock Units	417,700,000	366,400,000
Grant Price Range 1 [Member]
Summary Information By Grant Price Range For Stock Options And SARs Outstanding And Exercisable At End Of Period [Line Items]
Stock Options And Sars Outstanding	1,431,000
Weighted Average Remaining Life For Outstanding Options and SARs	1
Weighted Average Grant Price For Outstanding Options and SARs	$ 20.30
Number Of Exercisable Options and SARs	1,431,000
Weighted Average Grant Price For Exercisable Options and SARs	$ 20.30
Weighted Average Remaining Life For Exercisable Options and SARs	1
Grant Price Range 2 [Member]
Summary Information By Grant Price Range For Stock Options And SARs Outstanding And Exercisable At End Of Period [Line Items]
Stock Options And Sars Outstanding	1,623,000
Weighted Average Remaining Life For Outstanding Options and SARs	1
Weighted Average Grant Price For Outstanding Options and SARs	$ 61.99
Number Of Exercisable Options and SARs	1,609,000
Weighted Average Grant Price For Exercisable Options and SARs	$ 61.94
Weighted Average Remaining Life For Exercisable Options and SARs	1
Grant Price Range 3 [Member]
Summary Information By Grant Price Range For Stock Options And SARs Outstanding And Exercisable At End Of Period [Line Items]
Stock Options And Sars Outstanding	1,674,000
Weighted Average Remaining Life For Outstanding Options and SARs	4
Weighted Average Grant Price For Outstanding Options and SARs	$ 78.17
Number Of Exercisable Options and SARs	1,159,000
Weighted Average Grant Price For Exercisable Options and SARs	$ 76.66
Weighted Average Remaining Life For Exercisable Options and SARs	4
Grant Price Range 4 [Member]
Summary Information By Grant Price Range For Stock Options And SARs Outstanding And Exercisable At End Of Period [Line Items]
Stock Options And Sars Outstanding	2,174,000
Weighted Average Remaining Life For Outstanding Options and SARs	6
Weighted Average Grant Price For Outstanding Options and SARs	$ 85.44
Number Of Exercisable Options and SARs	576,000
Weighted Average Grant Price For Exercisable Options and SARs	$ 88.73
Weighted Average Remaining Life For Exercisable Options and SARs	4
Grant Price Range 5 [Member]
Summary Information By Grant Price Range For Stock Options And SARs Outstanding And Exercisable At End Of Period [Line Items]
Stock Options And Sars Outstanding	1,472,000
Weighted Average Remaining Life For Outstanding Options and SARs	5
Weighted Average Grant Price For Outstanding Options and SARs	$ 95.09
Number Of Exercisable Options and SARs	373,000
Weighted Average Grant Price For Exercisable Options and SARs	$ 96.56
Weighted Average Remaining Life For Exercisable Options and SARs	5
Lease And Well [Member]
Stock based compensation by job function [Line Items]
Compensation expense related to the company's stock-based compensation plans	33,000,000	27,000,000	23,000,000
Gathering And Processing Costs [Member]
Stock based compensation by job function [Line Items]
Compensation expense related to the company's stock-based compensation plans	1,000,000	1,000,000	0
Exploration Costs [Member]
Stock based compensation by job function [Line Items]
Compensation expense related to the company's stock-based compensation plans	26,000,000	24,000,000	21,000,000
General And Administrative [Member]
Stock based compensation by job function [Line Items]
Compensation expense related to the company's stock-based compensation plans	68,000,000	55,000,000	51,000,000
Pension Plans Defined Benefit and Contribution [Member]
Defined Benefit and Defined Contribution Plan Disclosure [Line Items]
Total pension plan costs	27,100,000	23,400,000	21,800,000
Company contributions to foreign pension plans	2,500,000	2,800,000	2,600,000
Benefit obligation	11,300,000	10,300,000
Accrued benefit cost	(1,600,000)	(800,000)
Fair value of foreign pension plan assets	8,200,000	8,700,000
Defined Benefit Plan Disclosure [Line Items]
Fair value of foreign pension plan assets	$ 8,200,000	$ 8,700,000