Stock-Based Compensation Plans (Details 4) (Employee Stock Purchase Plan, USD $) In Millions, except Per Share data, unless otherwise specified	9 Months Ended
	Sep. 30, 2012
Employee Stock Purchase Plan
Stock-Based Compensation Plans - Disclosures
Share purchases under employee stock purchase plan (in shares)	0.5
Weighted-average fair value of discount on employee stock purchase plan (in dollars per share)	$ 4.76
Shares available to be issued under employee stock purchase plan (in shares)	6.4