Income per Share (Tables)

12 Months Ended

Dec. 31, 2011

Income per Share [Abstract]

Reconciliation of the number of shares used for the basic and diluted income per share calculations

Millions of shares	2011		2010		2009
Basic weighted average common shares outstanding		918		908		900
Dilutive effect of stock options		4		3		2
Diluted weighted average common shares outstanding		922		911		902