CONSOLIDATED BALANCE SHEETS (Parenthetical) (USD $)	Mar. 31, 2013	Dec. 31, 2012
Common stock voting, par value (in dollars per share)	$ 0.0025	$ 0.0025
Common stock voting, shares authorized (in shares)	900,000,000	900,000,000
Common stock voting, shares issued (in shares)	256,333,083	255,592,901
Common stock voting, shares outstanding (in shares)	220,333,057	219,522,655
Treasury stock, shares (in shares)	36,000,026	36,070,246