Consolidated Statements of Changes in Stockholders' Equity (Parenthetical) (USD $) In Millions, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Consolidated Statements of Changes in Stockholders' Equity
Issuance of common stock for stock options, shares		111,792	125,268
Issuance of common stock for restricted share awards, shares	670,933	787,399	317,489
Issuance of common stock for employee stock unit awards, shares	71,580	288,917	311,106
Issuance of common stock for stock options, restricted share awards and employee stock unit awards, tax benefit shortfall (in dollars)	$ 4.1	$ 3.3	$ 2.2
Awards reclassified to liability for cash settlement, shares	259,840
Issuance of common stock for the employee stock purchase plan, shares	137,782	108,621	108,454
Purchase of common stock for treasury, shares	2,470,000	2,974,200	3,151,828
Shares withheld for net settlements of share-based awards, shares	270,467	369,099	235,075