Stockholders' Equity (Tables)

12 Months Ended

Dec. 31, 2012

Table Text Block [Abstract]

Common Stock Rollforward

millions	2012	2011	2010
Shares of common stock issued
Shares at January 1	516	513	509
Exercise of stock options	1	1	2
Issuance of restricted stock	2	2	2
Shares at December 31	519	516	513
Shares of common stock held in treasury
Shares at January 1	18	17	16
Shares received for restricted stock vested and options exercised	—	1	1
Shares at December 31	18	18	17
Shares of common stock outstanding at December 31	501	498	496

Earnings Per Share Table

			Years Ended December 31,
millions except per-share amounts			2012		2011		2010
Net income (loss)
	Net income (loss) attributable to common stockholders		$	2,391	$	(2,649)	$	761
	Less distributions on participating securities			1		—		1
	Less undistributed income allocated to participating securities			14		—		4
	Basic		$	2,376	$	(2,649)	$	756
	Diluted		$	2,376	$	(2,649)	$	756
Shares
	Average number of common shares outstanding—basic			500		498		495
		Dilutive effect of stock options and performance-based stock awards		2		—		2
	Average number of common shares outstanding—diluted			502		498		497
	Excluded (1)			6		12		6
Net income (loss) per common share
	Basic		$	4.76	$	(5.32)	$	1.53
	Diluted		$	4.74	$	(5.32)	$	1.52
	Dividends per common share		$	0.36	$	0.36	$	0.36

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(1) Inclusion of certain shares would have had an anti-dilutive effect.