Equity - Earnings Per Share (Details) $ / shares in Units, shares in Millions, $ in Millions		3 Months Ended								12 Months Ended
	May 09, 2017	Dec. 31, 2017 USD ($) $ / shares shares	Sep. 30, 2017 USD ($) $ / shares shares	Jun. 30, 2017 USD ($) $ / shares shares	Mar. 31, 2017 USD ($) $ / shares shares	Dec. 31, 2016 USD ($) $ / shares shares	Sep. 30, 2016 USD ($) $ / shares shares	Jun. 30, 2016 USD ($) $ / shares shares	Mar. 31, 2016 USD ($) $ / shares shares	Dec. 31, 2017 USD ($) $ / shares shares	Dec. 31, 2016 USD ($) $ / shares shares	Dec. 31, 2015 USD ($) $ / shares shares
Treasury shares, stock split										16.5
Income from continuing operations attributable to DST Systems, Inc. | $										$ 447.0	$ 179.0	$ 309.7
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
Net income attributable to DST Systems, Inc. | $		$ 81.2	$ 48.5	$ 75.4	$ 246.4	$ 42.9	$ 273.3	$ 53.0	$ 58.1	$ 451.5	$ 427.3	$ 358.2
Weighted average common shares outstanding		59.9	60.7	61.9	63.1	64.2	65.4	66.6	67.6	61.4	66.0	72.0
Incremental shares from restricted stock units and stock options										0.7	0.6	0.9
Weighted average diluted shares outstanding		60.6	61.6	62.5	63.9	65.0	66.1	67.2	68.5	62.1	66.6	72.9
Basic earnings per share
Continuing operations attributable to DST Systems, Inc., per basic share (in dollars per share) | $ / shares		$ 1.36	$ 0.81	$ 1.19	$ 3.86	$ 0.85	$ 0.77	$ 0.52	$ 0.59	$ 7.28	$ 2.71	$ 4.30
Discontinued operation, per basic share (in dollars per share) | $ / shares		0.00	(0.01)	0.03	0.05	(0.18)	3.41	0.28	0.27	0.07	3.76	0.67
Basic earnings per share (in dollars per share) | $ / shares		1.36	0.80	1.22	3.91	0.67	4.18	0.80	0.86	7.35	6.47	4.97
Diluted earnings per share
Continuing operations attributable to DST Systems, Inc., per diluted share (in dollars per share) | $ / shares		1.34	0.79	1.18	3.81	0.84	0.76	0.51	0.59	7.20	2.68	4.25
Discontinued operation, per diluted share (in dollars per share) | $ / shares		0.00	0.00	0.03	0.04	(0.18)	3.37	0.28	0.26	0.07	3.73	0.67
Diluted earnings per share (in dollars per share) | $ / shares		$ 1.34	$ 0.79	$ 1.21	$ 3.85	$ 0.66	$ 4.13	$ 0.79	$ 0.85	$ 7.27	$ 6.41	$ 4.92
Shares outstanding		59.3				64.0				59.3	64.0
Shares from options to purchase common stock, excluded from diluted earnings per share calculation										0.0	0.0
Preferred stock, shares authorized		10.0				10.0				10.0	10.0
Preferred stock, shares issued		0.0				0.0				0.0	0.0
Preferred Stock, shares outstanding		0.0								0.0
Common Stock
Stock split, conversion ratio	2