Discontinued Operations - Disposal Group Income Statement (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Income from discontinued operations, net of tax	$ 0.0	$ (0.3)	$ 1.9	$ 2.9	$ (11.7)	$ 222.8	$ 18.7	$ 18.5	$ 4.5	$ 248.3	$ 48.5
Customer Communications | Discontinued Operations, Held-for-sale
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Operating revenues									53.4	389.0	608.0
Out-of-pocket reimbursements									12.8	409.0	743.1
Total revenue									66.2	798.0	1,351.1
Costs and expense									63.8	747.6	1,247.3
Depreciation and amortization (including goodwill impairment)									0.0	28.9	30.9
Operating income									2.4	21.5	72.9
Interest expense									0.0	0.0	(0.3)
Equity in earnings of unconsolidated affiliates									0.2	0.3	0.4
Net gain on business disposition									2.6	341.5	0.0
Income before income taxes									5.2	363.3	73.0
Income taxes									0.7	115.0	24.5
Income from discontinued operations, net of tax									$ 4.5	$ 248.3	$ 48.5