Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Millions	Sep. 30, 2015	Dec. 31, 2014
Accounts receivable, allowance for doubtful accounts and billing adjustments	$ 4.8	$ 5.2
Computer software, accumulated amortization	661.9	613.3
Other intangible assets, accumulated amortization	238.3	181.9
Property and equipment, accumulated depreciation and amortization	449.5	423.2
Contract acquisition costs, accumulated amortization	$ 304.6	$ 276.1
Common stock, par value	$ 0.10	$ 0.10
Common stock, authorized	600,000,000	600,000,000
Common stock, issued	202,770,000	202,775,000
Common stock, outstanding	183,978,000	184,939,000
Treasury stock, shares	18,792,000	17,836,000