Segment Information (Details) $ in Millions	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2017 USD ($)	Sep. 30, 2016 USD ($)	Sep. 30, 2017 USD ($)	Sep. 30, 2016 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Segment Reporting [Abstract]
Number of operating segments			3
Summary of financial information of segments [Line Items]
Total assets	$ 3,002.2		$ 3,002.2		$ 2,771.8
Operating revenues	524.8	$ 365.5	1,534.0	$ 1,100.7
Out-of-pocket reimbursements	37.8	21.2	90.3	57.2	82.3	$ 69.0
Total revenues	562.6	386.7	1,624.3	1,157.9	1,556.7	1,474.0
Costs and expenses	472.1	289.6	1,323.7	916.9	1,213.4	1,150.2
Depreciation and amortization	34.7	22.8	92.7	69.1	96.0	91.1
Operating income	55.8	74.3	207.9	171.9	247.3	232.7
Other income (loss), net	8.7	6.7	217.2	20.0	22.7	204.5
Gain on sale of business					5.5
Equity in earnings of unconsolidated affiliates	4.2	7.0	27.3	23.9	27.2	45.4
Earnings from continuing operations before interest, income taxes and non-controlling interest	68.7	88.0	452.4	215.8	302.7	482.6
Interest expense	(6.9)	(5.4)	(19.7)	(18.0)	(23.5)	(23.8)
Operating Segments
Summary of financial information of segments [Line Items]
Operating revenues	524.8	365.5	1,534.0	1,100.7	1,474.4	1,405.0
Operating Segments | Domestic Financial Services
Summary of financial information of segments [Line Items]
Total assets	2,332.4		2,332.4		2,234.9
Operating revenues	291.4	232.6	827.9	704.3	937.7	936.8
Out-of-pocket reimbursements	28.8	19.2	77.6	50.5	73.0	60.7
Total revenues	334.1	266.6	948.9	798.1	1,068.8	1,043.8
Costs and expenses	275.9	194.9	783.6	629.9	829.0	792.3
Depreciation and amortization	22.6	18.0	63.3	54.9	77.3	67.7
Operating income	35.6	53.7	102.0	113.3	162.5	183.8
Other income (loss), net	8.8	4.1	229.2	11.9	13.9	207.2
Gain on sale of business					0.0
Equity in earnings of unconsolidated affiliates	1.7	2.5	10.1	11.4	14.3	23.8
Earnings from continuing operations before interest, income taxes and non-controlling interest	46.1	60.3	341.3	136.6	190.7	414.8
Operating Segments | International Financial Services
Summary of financial information of segments [Line Items]
Total assets	749.5		749.5		430.0
Operating revenues	129.2	26.8	392.9	82.1	110.5	91.8
Out-of-pocket reimbursements	7.1	0.2	7.4	0.8	1.2	1.7
Total revenues	136.5	27.1	400.7	83.2	112.1	95.1
Costs and expenses	125.0	23.6	328.1	72.9	98.2	86.1
Depreciation and amortization	9.7	1.0	21.3	2.2	3.1	4.8
Operating income	1.8	2.5	51.3	8.1	10.8	4.2
Other income (loss), net	(0.3)	2.5	(12.2)	8.0	8.7	(2.6)
Gain on sale of business					5.5
Equity in earnings of unconsolidated affiliates	2.4	4.4	16.8	12.3	12.4	21.3
Earnings from continuing operations before interest, income taxes and non-controlling interest	3.9	9.4	55.9	28.4	37.4	22.9
Operating Segments | Healthcare Services
Summary of financial information of segments [Line Items]
Total assets	500.2		500.2		552.2
Operating revenues	104.2	106.1	313.2	314.3	426.2	376.4
Out-of-pocket reimbursements	1.9	1.8	5.5	6.3	8.5	8.2
Total revenues	106.1	107.9	318.7	320.6	434.7	384.6
Costs and expenses	85.3	86.0	256.0	258.1	345.1	321.3
Depreciation and amortization	2.4	3.8	8.1	12.0	15.6	18.6
Operating income	18.4	18.1	54.6	50.5	74.0	44.7
Other income (loss), net	0.2	0.1	0.2	0.1	0.1	(0.1)
Gain on sale of business					0.0
Equity in earnings of unconsolidated affiliates	0.1	0.1	0.4	0.2	0.5	0.3
Earnings from continuing operations before interest, income taxes and non-controlling interest	18.7	18.3	55.2	50.8	74.6	44.9
Elimination Adjustments
Summary of financial information of segments [Line Items]
Total assets	(579.9)		(579.9)		(517.9)
Operating revenues	(14.1)	(14.9)	(43.8)	(43.6)	(58.5)	(47.9)
Out-of-pocket reimbursements	0.0	0.0	(0.2)	(0.4)	(0.4)	(1.6)
Total revenues	(14.1)	(14.9)	(44.0)	(44.0)	(58.9)	(49.5)
Costs and expenses	(14.1)	(14.9)	(44.0)	(44.0)	(58.9)	(49.5)
Depreciation and amortization	0.0	0.0	0.0	0.0	0.0	0.0
Operating income	0.0	0.0	0.0	0.0	0.0	0.0
Other income (loss), net	0.0	0.0	0.0	0.0	0.0	0.0
Gain on sale of business					0.0
Equity in earnings of unconsolidated affiliates	0.0	0.0	0.0	0.0	0.0	0.0
Earnings from continuing operations before interest, income taxes and non-controlling interest	0.0	0.0	0.0	0.0	0.0	0.0
Elimination Adjustments | Domestic Financial Services
Summary of financial information of segments [Line Items]
Operating revenues	13.9	14.8	43.4	43.3	58.1	46.3
Elimination Adjustments | International Financial Services
Summary of financial information of segments [Line Items]
Operating revenues	0.2	0.1	0.4	0.3	0.4	1.6
Elimination Adjustments | Healthcare Services
Summary of financial information of segments [Line Items]
Operating revenues	0.0	$ 0.0	0.0	$ 0.0	0.0	$ 0.0
Discontinued Operations, Held-for-sale | Customer Communications
Summary of financial information of segments [Line Items]
Assets held for sale	$ 0.0		$ 0.0		$ 72.6