Stockholders' Equity (Tables)

12 Months Ended

Dec. 31, 2015

Stockholders' Equity Note [Abstract]

Schedule of Share Repurchases [Table Text Block]

Share repurchases were as follows:

	Years Ended December 31,
	2015		2014		2013
Shares repurchased in the open market	8,228,542		7,467,228		6,005,880
Shares repurchased from holders of employee stock options	—		—		5,951
Total shares repurchased	8,228,542		7,467,228		6,011,831
Average price paid per share	$	72.94	$	80.50	$	76.16