Basic and Diluted Earnings Per Share (Details) (USD $) In Millions, except Per Share data	3 Months Ended				9 Months Ended
	Sep. 30, 2011		Sep. 30, 2010		Sep. 30, 2011		Sep. 30, 2010
Basic and Diluted Earnings Per Share [Abstract]
Net Income	$ 441		$ 232		$ 749		$ 673
Earnings Adjustment from Assumed Conversion of Dilutive Shares of Common Stock in Rabbi Trust	(12)	[1]	0	[1]	(10)	[1]	3	[1]
Net Income Used for Diluted Earnings Per Share Calculation	$ 429		$ 232		$ 739		$ 676
Weighted Average Number of Shares Outstanding, Basic (in shares)	177		175		176		175
Incremental Shares from Assumed Conversion of Dilutive Stock Options, Restricted Stock and Shares of Common Stock in Rabbi Trust (in shares)	3		2		3		3
Weighted Average Number of Shares Outstanding, Diluted (in shares)	180		177		179		178
Earnings Per Share, Basic (in dollars per share)	$ 2.50		$ 1.33		$ 4.25		$ 3.86
Earnings Per Share, Diluted (in dollars per share)	$ 2.39		$ 1.31		$ 4.12		$ 3.80
Number of antidilutive stock options and shares of restricted stock excluded from calculation above	1		2		2		2

[1] Consistent with GAAP, when dilutive, deferred compensation gains or losses, net of tax, are excluded from net income while the NBL shares held in the rabbi trust are included in the diluted share count. For this reason, the diluted earnings per share calculations for the three and nine months ended September 30, 2011 exclude deferred compensation gains, net of tax; and the diluted earnings per share calculation for the nine months ended September 30, 2010 excludes a deferred compensation loss, net of tax.