Stockholders' Equity (Tables)

12 Months Ended

Dec. 31, 2014

Stockholders' Equity Note [Abstract]

Schedule of Share Repurchases [Table Text Block]

Share repurchases were as follows:

	Years Ended December 31,
	2014		2013		2012
Shares repurchased in the open market	7,467,228		6,005,880		12,314,795
Shares repurchased from holders of employee stock options	—		5,951		86,303
Total shares repurchased	7,467,228		6,011,831		12,401,098
Average price paid per share	$	80.50	$	76.16	$	60.38