Stock-Based Compensation Plans (Details 2) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Allocation of recognized period costs of employee service share-based compensation
Stock based compensation expense, gross	$ 10.4	$ 8.3	$ 19.7	$ 19.3
Stock based compensation expense, net of tax	7.1	5.7	13.5	13.3
Tax benefit on stock based compensation	3.3	2.6	6.2	6.0
Cost of revenue
Allocation of recognized period costs of employee service share-based compensation
Stock based compensation expense, gross	4.6	3.4	8.6	8.5
Selling, general and administrative expenses
Allocation of recognized period costs of employee service share-based compensation
Stock based compensation expense, gross	$ 5.8	$ 4.9	$ 11.1	$ 10.8