Employee Benefit Plans (Details) (USD $)	12 Months Ended
	Dec. 31, 2012 Y	Dec. 31, 2011	Dec. 31, 2010
Stock based compensation by job function [Line Items]
Compensation expense related to the company's stock-based compensation plans	$ 127,504,000	$ 128,205,000	$ 107,314,000
Maximum shares of stock-based awards approved	12,900,000
Common Shares Available for Grant	3,400,000
Federal income tax (expense) / benefit recognized from stock-based compensation	67,000,000	25,000	(1,000,000)
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	49,000,000	48,000,000	41,000,000
Share-Based Compensation Arrangement By Share-Based Payment Award[Abstract]
Available for Future Grant (in shares)	3,400,000
Stock options/SARs vested or expected to vest (in shares)	5,982,406
Weighted average grant price for stock options/SARs vested or expected to vest (per share)	$ 85.36
Intrinsic value of stock options/SARs vested or expected to vest	212,000,000
Weighted Average Remaining Contractual Life for Stock Options/SARs Vested or Expected to Vest	4.1
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	6,219,000
Weighted Average Remaining Life for Outstanding Options and SARs	4
Weighted Average Grant Price For Outstanding Options and SARs	$ 85.81
Aggregate Intrinsic Value For Outstanding Options and SARs	217,879,000
Stock Options and SARs Exercisable	3,143,000
Weighted Average Remaining Life For Exercisable Units	3
Weighted Average Grant Price For Exercisable Options and SARs	$ 74.98
Aggregate Intrinsic Value For Exercisable Units	144,335,000
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	846,000
Weighted Average Remaining Life for Outstanding Options and SARs	1
Weighted Average Grant Price For Outstanding Options and SARs	$ 45.84
Stock Options and SARs Exercisable	838,000
Weighted Average Remaining Life For Exercisable Units	1
Weighted Average Grant Price For Exercisable Options and SARs	$ 45.62
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	1,168,000
Weighted Average Remaining Life for Outstanding Options and SARs	3
Weighted Average Grant Price For Outstanding Options and SARs	$ 78.44
Stock Options and SARs Exercisable	932,000
Weighted Average Remaining Life For Exercisable Units	3
Weighted Average Grant Price For Exercisable Options and SARs	$ 77.64
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	1,767,000
Weighted Average Remaining Life for Outstanding Options and SARs	5
Weighted Average Grant Price For Outstanding Options and SARs	$ 85.14
Stock Options and SARs Exercisable	790,000
Weighted Average Remaining Life For Exercisable Units	4
Weighted Average Grant Price For Exercisable Options and SARs	$ 87.14
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	1,157,000
Weighted Average Remaining Life for Outstanding Options and SARs	4
Weighted Average Grant Price For Outstanding Options and SARs	$ 93.37
Stock Options and SARs Exercisable	508,000
Weighted Average Remaining Life For Exercisable Units	4
Weighted Average Grant Price For Exercisable Options and SARs	$ 92.76
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	1,281,000
Weighted Average Remaining Life for Outstanding Options and SARs	6
Weighted Average Grant Price For Outstanding Options and SARs	$ 113.03
Stock Options and SARs Exercisable	75,000
Weighted Average Remaining Life For Exercisable Units	4
Weighted Average Grant Price For Exercisable Options and SARs	$ 121.24
Stock Options And Sars [Member]
Weighted Average Fair Value And Valuation Assumptions Used To Value Stock-Based Compensation [Abstract]
Weighted Average Fair Value of Grants	$ 37.95	$ 29.92	$ 32.12
Expected Volatility (in hundredths)	39.68%	40.96%	39.70%
Risk-Free Interest Rate (in hundredths)	0.45%	0.58%	0.87%
Dividend Yield (in hundredths)	0.60%	0.70%	0.70%
Expected Life (in years)	5.6	5.6	5.5
Stock option and SAR Rollforward [Abstract]
Outstanding at January 1	8,374,000	8,445,000	8,335,000
Granted	1,240,000	1,509,000	1,450,000
Exercised (1)	(3,246,000)	(1,399,000)	(1,144,000)
Forfeited	(149,000)	(181,000)	(196,000)
Outstanding at December 31	6,219,000	8,374,000	8,445,000
Share-Based Compensation Arrangement By Share-Based Payment Award[Abstract]
Outstanding at January 1 - Price per Share	$ 70.01	$ 64.49	$ 57.08
Granted - Price Per Share	$ 111.97	$ 85.29	$ 93.07
Exercised - Price Per Share	$ 54.80	$ 50.86	$ 43.38
Forfeited - Price per Share	$ 91.18	$ 87.74	$ 84.22
Outstanding at December 31 - Price per Share	$ 85.81	$ 70.01	$ 64.49
Stock Options/SARs Exercisable at December 31 (in shares)	3,143,000	5,148,000	5,439,000
Stock Options/SARs Exercisable at December 31 (price per share)	$ 74.98	$ 59.19	$ 51.71
Intrinsic value of stock options/SARs exercised during the period	185,000,000	78,000,000	66,000,000
Unrecognized compensation expense	91,000,000
Weighted average period over which unrecognized compensation expense will be recognized (in years)	2.8
Espp [Member]
Stock based compensation by job function [Line Items]
Common Shares Available for Grant	625,000
Weighted Average Fair Value And Valuation Assumptions Used To Value Stock-Based Compensation [Abstract]
Weighted Average Fair Value of Grants	$ 25.11	$ 22.75	$ 25.45
Expected Volatility (in hundredths)	40.92%	29.82%	38.30%
Risk-Free Interest Rate (in hundredths)	0.11%	0.14%	0.18%
Dividend Yield (in hundredths)	0.60%	0.70%	0.70%
Expected Life (in years)	0.5	0.5	0.5
Share-Based Compensation Arrangement By Share-Based Payment Award[Abstract]
Available for Future Grant (in shares)	625,000
Approximate Number of Participants	1,705	1,525	1,236
Shares Purchased	164,000	135,000	114,000
Aggregate Purchase Price	12,522,000	10,947,000	9,172,000
Restricted Stock And Restricted Stock Units [Member]
Share-Based Compensation Arrangement By Share-Based Payment Award[Abstract]
Unrecognized compensation expense	136,000,000
Weighted average period over which unrecognized compensation expense will be recognized (in years)	2.5
Share Based Compensation Arrangement By Restricted Stock And Restricted Stock Units Compensation Cost	72,000,000	80,000,000	66,000,000
Restricted Stock and Restricted Stock Unit [Roll Forward]
Outstanding at January 1	4,240,000	4,009,000	3,636,000
Granted	767,000	932,000	850,000
Released (1)	(1,059,000)	(457,000)	(364,000)
Forfeited	(130,000)	(244,000)	(113,000)
Outstanding at December 31 (2)	3,818,000	4,240,000	4,009,000
Weighted Average Grant Price Restricted Stock and Restricted Stock Units Rollforward [Abstract]
Outstanding at January 1 (price per share)	$ 82.93	$ 79.13	$ 73.69
Granted (price per share)	$ 112.17	$ 90.87	$ 93.39
Released (1) (price per share)	$ 72.70	$ 66.10	$ 58.00
Forfeited (price per share)	$ 85.36	$ 82.45	$ 79.37
Outstanding at December 31 (2) (price per share)	$ 91.06	$ 82.93	$ 79.13
Intrinsic value of restricted stock and restricted stock units released during the year	120,000,000	44,000,000	35,000,000
Aggregate Intrinsic Value Of Restricted Stock And Restricted Stock Units	461,000,000	418,000,000
Performance Units and Performance Stock [Member]
Weighted Average Fair Value And Valuation Assumptions Used To Value Stock-Based Compensation [Abstract]
Weighted Average Fair Value of Grants	$ 134.09
Expected Volatility (in hundredths)	36.39%
Risk-Free Interest Rate (in hundredths)	0.39%
Dividend Yield (in hundredths)	0.60%
Share-Based Compensation Arrangement By Share-Based Payment Award[Abstract]
Unrecognized compensation expense	3,000,000
Weighted average period over which unrecognized compensation expense will be recognized (in years)	3.0
Performance Units and Performance Stock [Abstract]
Performance Units Granted	54,526
Performance Stock Granted	16,752
Minimum Performance Units and Stock Allowed to be Outstanding	0
Maximum Performance Units And Stock Allowed To Be Outstanding	142,556
Share Based Compensation Arrangement By Performance Units and Stock Compensation Cost	7,000,000
Term of Zero-Coupon Risk-Free Interest Rate (in years) Derived from the Treasury Constant Maturities Yield Curve	3.26
Lease And Well [Member]
Stock based compensation by job function [Line Items]
Compensation expense related to the company's stock-based compensation plans	35,000,000	33,000,000	27,000,000
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	1,000,000
Exploration Costs [Member]
Stock based compensation by job function [Line Items]
Compensation expense related to the company's stock-based compensation plans	27,000,000	26,000,000	24,000,000
General And Administrative [Member]
Stock based compensation by job function [Line Items]
Compensation expense related to the company's stock-based compensation plans	65,000,000	68,000,000	55,000,000
Pension Plans Defined Benefit and Contribution [Member]
Defined Benefit and Defined Contribution Plan Disclosure [Line Items]
Total pension plan costs	36,000,000	27,000,000	23,000,000
Company contributions to foreign pension plans	3,000,000	3,000,000	3,000,000
Benefit obligation	14,000,000	11,000,000
Fair value of foreign pension plan assets	10,000,000	8,000,000
Accrued benefit cost	$ (2,000,000)	$ (2,000,000)