Quarterly Financial Data (Unaudited) (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016		Dec. 31, 2015		Dec. 31, 2014
Quarterly Financial Information Disclosure [Abstract]
Operating revenues	$ 373.7	$ 365.5	$ 373.9	$ 361.3	$ 362.3	$ 353.4	$ 349.3	$ 340.0	$ 1,474.4		$ 1,405.0		$ 1,445.5
Out-of-pocket reimbursements	25.1	21.2	16.6	19.4	20.9	18.2	14.2	15.7	82.3		69.0		59.3
Total revenues	398.8	386.7	390.5	380.7	383.2	371.6	363.5	355.7	1,556.7		1,474.0		1,504.8
Costs and expenses	296.5	289.6	320.4	306.9	295.9	287.1	289.7	277.5	1,213.4		1,150.2		1,149.1
Depreciation and amortization	26.9	22.8	24.2	22.1	25.1	22.9	21.7	21.4	96.0		91.1		93.0
Operating income	75.4	74.3	45.9	51.7	62.2	61.6	52.1	56.8	247.3		232.7		262.7
Interest expense	(5.5)	(5.4)	(6.5)	(6.1)	(6.1)	(5.8)	(5.8)	(6.1)	(23.5)		(23.8)		(26.3)
Gain on sale of business	5.5	0.0	0.0	0.0					5.5		0.0		100.5
Other income, net	2.7	6.7	7.0	6.3	14.6	14.4	92.2	83.3	22.7		204.5		373.1
Equity in earnings of unconsolidated affiliates	3.3	7.0	10.2	6.7	6.2	11.8	12.7	14.7	27.2		45.4		34.7
Income from continuing operations before income taxes and non-controlling interest	81.4	82.6	56.6	58.6	76.9	82.0	151.2	148.7	279.2		458.8		744.7
Income taxes	27.3	31.6	22.1	20.1	22.0	15.9	55.7	55.6	101.1		149.2		183.9
Income from continuing operations before non-controlling interest	54.1	51.0	34.5	38.5	54.9	66.1	95.5	93.1	178.1		309.6		560.8
Income from discontinued operations, net of tax	(11.7)	222.8	18.7	18.5	12.8	9.0	12.0	14.7	248.3		48.5		32.5
Net income	42.4	273.8	53.2	57.0	67.7	75.1	107.5	107.8	426.4		358.1		593.3
Net loss attributable to non-controlling interest	0.5	(0.5)	(0.2)	1.1	0.1	0.0	0.0	0.0	0.9		0.1		0.0
Net income attributable to DST Systems, Inc.	$ 42.9	$ 273.3	$ 53.0	$ 58.1	$ 67.8	$ 75.1	$ 107.5	$ 107.8	$ 427.3		$ 358.2		$ 593.3
Weighted average common shares outstanding	32.1	32.7	33.3	33.8	34.5	35.7	36.6	37.2	33.0		36.0		40.0
Weighted average diluted shares outstanding	32.5	33.0	33.6	34.3	35.0	36.2	37.0	37.6	33.3		36.4		40.5
Continuing operations attributable to DST Systems, Inc., per basic share (in dollars per share)	$ 1.70	$ 1.54	$ 1.03	$ 1.17	$ 1.59	$ 1.85	$ 2.61	$ 2.50	$ 5.43	[1]	$ 8.60	[1]	$ 14.01
Discontinued operation, per basic share (in dollars per share)	(0.36)	6.81	0.56	0.55	0.37	0.25	0.33	0.40	7.53	[1]	1.35	[1]	0.81
Basic earnings per share (in dollars per share)	1.34	8.35	1.59	1.72	1.96	2.10	2.94	2.90	12.96	[1]	9.95	[1]	14.82
Continuing operations attributable to DST Systems, Inc., per diluted share (in dollars per share)	1.68	1.53	1.03	1.16	1.57	1.83	2.58	2.48	5.37	[1]	8.50	[1]	13.86
Discontinued operation, per diluted share (in dollars per share)	(0.36)	6.75	0.55	0.54	0.37	0.25	0.33	0.39	7.45	[1]	1.33	[1]	0.80
Diluted earnings per share (in dollars per share)	1.32	8.28	1.58	1.70	1.94	2.08	2.91	2.87	12.82	[1]	9.83	[1]	14.66
Cash dividends per share of common stock (in dollars per share)	$ 0.33	$ 0.33	$ 0.33	$ 0.33	$ 0.30	$ 0.30	$ 0.30	$ 0.30	$ 1.32		$ 1.20		$ 1.20

[1] Earnings per share are computed independently for each of the quarters presented. Accordingly, the accumulation of quarterly earnings per share may not equal the total computed for the year.