Significant Business Transactions and Events - Acquisition of IFDS U.K., Schedule of Aggregate Acquisition-date Fair Value of Consideration Transferred (Details) - USD ($) $ in Millions		1 Months Ended
	Mar. 27, 2017	Mar. 31, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Recognized Amounts of Identifiable Assets Acquired and Liabilities Assumed
Goodwill			$ 799.1	$ 516.4	$ 458.3
IFDS U.K. IFDS, Percana and IFDS Realty U.K.
Consideration
Cash paid	$ 234.9
Estimated fair value of DST's previously-held equity interests	136.8
Effective settlement of pre-existing relationships	54.5
Total consideration transferred	426.2
Recognized Amounts of Identifiable Assets Acquired and Liabilities Assumed
Cash and cash equivalents	99.2
Accounts receivable	101.7
Other current assets	14.4
Properties	94.7
Intangible assets	104.0
Goodwill	196.7
Deferred income taxes	11.6
Other assets	2.1
Total assets	624.4
Current portion of long-term debt	2.8
Accounts payable	29.1
Accrued compensation and benefits	23.6
Deferred revenue	31.1
Other current liabilities	61.7
Long-term debt	26.3
Other liabilities	23.6
Total liabilities	198.2
Net assets acquired	426.2
International Financial Data Services U.K.
Consideration
Cash paid	141.0
Recognized Amounts of Identifiable Assets Acquired and Liabilities Assumed
Goodwill	$ 196.7
Acquisition price discount (as a percent)	3.00%
Acquired software | International Financial Data Services U.K.
Recognized Amounts of Identifiable Assets Acquired and Liabilities Assumed
Properties	$ 21.0
Weighted average useful life		6 years