Income Taxes - Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Deferred tax assets:
Equity compensation plans	$ 17.7	$ 18.7
Payroll and benefits	9.3	8.0
Deferred interest	0.0	6.8
Net operating loss and credit carryforwards, net	23.8	28.1
Rent	7.5	7.4
Accounts receivable	6.5	5.4
Other	10.0	9.5
Total deferred tax assets	74.8	83.9
Deferred tax liabilities:
Software and intangibles	148.6	194.5
Deferred income	0.0	18.6
International investments	19.2	19.2
Property and equipment	20.0	20.4
Other	11.7	12.0
Total deferred tax liabilities	199.5	264.7
Deferred tax asset valuation allowance	17.2	15.5
Net deferred tax liabilities	$ 141.9	$ 196.3