Condensed Consolidated Statement of Comprehensive Income - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Statement of Comprehensive Income [Abstract]
Net income attributable to DST Systems, Inc.		$ 48.5	$ 273.3	$ 370.3	$ 384.4
Other comprehensive income (loss), net of tax and reclassifications to earnings, derived from:
Available-for-sale securities		0.3	21.7	(93.6)	(0.7)
Cash flow hedges		0.0	0.0	0.2	0.2
Foreign currency translation adjustments	[1]	16.0	(1.1)	69.1	(24.3)
Other comprehensive income (loss)		16.3	20.6	(24.3)	(24.8)
Comprehensive income		$ 64.8	$ 293.9	$ 346.0	$ 359.6

[1] Cumulative translation adjustments are inclusive of amounts derived from assets and liabilities held for sale.