Additional Shareholders' Equity Information (Details) (USD $) In Millions, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2008
Common stock shares issued [Rollforward]
Shares, beginning of period (in shares)	195,440,048	193,550,391
Exercise of common stock options (in shares)	837,096	1,502,454
Restricted stock awards, net of forfeitures (in shares)	379,702	387,203
Shares, end of period (in shares)	196,656,846	195,440,048	193,550,391
Treasury stock [Rollforward]
Shares, beginning of period (in shares)	18,650,064	18,582,301
Shares received from employees in payment of withholding taxes due on vesting of shares of restricted stock (in shares)	186,556	167,863
Rabbi trust shares sold (in shares)	(100,100)	(100,100)
Shares, end of period (in shares)	18,736,520	18,650,064	18,582,301
Components and changes in accumulated other comprehensive income (loss) [Abstract]
Beginning Balance	$ (104)	$ (75)	$ (110)
Realized Amounts Reclassified Into Earnings	5	16	39
Net Change in Other			(4)
Unrealized Change in Fair Value	(1)	(45)
End Balance	(100)	(104)	(75)	(110)
Effective income tax rate	35.00%	35.00%	35.00%	37.60%
Oil and gas cash flow hedges [Member]
Components and changes in accumulated other comprehensive income (loss) [Abstract]
Beginning Balance	0	(12)	(48)
Realized Amounts Reclassified Into Earnings	0	12	36
Net Change in Other			0
Unrealized Change in Fair Value	0	0
End Balance	0	0	(12)
Interest rate cash flow hedges [Member]
Components and changes in accumulated other comprehensive income (loss) [Abstract]
Beginning Balance	(42)	(2)	(3)
Realized Amounts Reclassified Into Earnings	1	1	1
Net Change in Other			0
Unrealized Change in Fair Value	15	(41)
End Balance	(26)	(42)	(2)
Pension-related and other [Member]
Components and changes in accumulated other comprehensive income (loss) [Abstract]
Beginning Balance	(62)	(61)	(59)
Realized Amounts Reclassified Into Earnings	4	3	2
Net Change in Other			(4)
Unrealized Change in Fair Value	(16)	(4)
End Balance	$ (74)	$ (62)	$ (61)