Significant Business Transactions and Events - Acquisition of IFDS U.K. (Details) - USD ($) $ in Millions		12 Months Ended
	Mar. 27, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Mar. 30, 2017
Business Acquisition [Line Items]
Acquisition of businesses, net of cash and cash equivalents acquired		$ 38.9	$ 93.5	$ 117.4
Goodwill		$ 799.1	$ 516.4	$ 458.3
International Financial Data Services U.K.
Business Acquisition [Line Items]
Cash paid	$ 141.0
Ownership percentage	50.00%
Payments to acquire notes receivable	$ 25.9
Remeasurement loss	12.2
Goodwill	196.7
Goodwill, expected tax deductible amount	18.9
IFDS Realty U.K. and IFDS Percana
Business Acquisition [Line Items]
Total consideration transferred	68.0
IFDS U.K. IFDS, Percana and IFDS Realty U.K.
Business Acquisition [Line Items]
Cash paid	234.9
Total consideration transferred	426.2
Acquisition of businesses, net of cash and cash equivalents acquired	175.0
Estimated fair value of DST's previously-held equity interests	136.8
Goodwill	$ 196.7
International Financial Data Services L.P.
Business Acquisition [Line Items]
Ownership percentage	50.00%	50.00%			50.00%