Consolidated Statement of Changes in Stockholders' Equity - USD ($) shares in Millions, $ in Millions	Total	Common Stock	Additional Paid-in Capital	Retained Earnings	Treasury Stock	Accumulated Other Comprehensive Income
Balance (in shares) at Dec. 31, 2014		75.2
Balance at Dec. 31, 2014	$ 1,236.4	$ 0.8	$ 114.1	$ 1,682.9	$ (748.3)	$ 186.9
Comprehensive income:
Net income attributable to DST Systems, Inc.	358.2			358.2
Other comprehensive loss	(145.0)					(145.0)
Dividends	(43.1)		(1.4)	(44.5)
Amortization of share-based compensation	27.9		27.9
Issuance of common stock (in shares)		0.6
Issuance of common stock	18.7		(5.2)		23.9
Repurchase of common stock (in shares)		(7.2)
Repurchase of common stock	(405.3)				(405.3)
Other	(1.8)		(1.8)
Balance (in shares) at Dec. 31, 2015		68.6
Balance at Dec. 31, 2015	1,046.0	$ 0.8	136.4	1,996.6	(1,129.7)	41.9
Comprehensive income:
Net income attributable to DST Systems, Inc.	427.3			427.3
Other comprehensive loss	(25.3)					(25.3)
Dividends	(43.4)		(1.3)	(44.7)
Amortization of share-based compensation	16.3		16.3
Issuance of common stock (in shares)		0.8
Issuance of common stock	10.4		(24.5)		34.9
Repurchase of common stock (in shares)		(5.4)
Repurchase of common stock	(315.8)				(315.8)
Other	(0.3)		(0.3)
Balance (in shares) at Dec. 31, 2016		64.0
Balance at Dec. 31, 2016	1,115.2	$ 0.8	129.2	2,379.2	(1,410.6)	16.6
Comprehensive income:
Net income attributable to DST Systems, Inc.	451.5			451.5
Other comprehensive loss	(15.2)					(15.2)
Dividends	(43.7)		(1.0)	(44.7)
Amortization of share-based compensation	44.2		44.2
Issuance of common stock (in shares)		0.4
Issuance of common stock	3.0		(21.2)		24.2
Repurchase of common stock (in shares)		(5.1)
Repurchase of common stock	(314.3)				(314.3)
Distribution of treasury stock for stock split	0.0	$ (0.2)	(40.5)	(1,297.2)	1,337.9
Other	0.5			(0.5)
Balance (in shares) at Dec. 31, 2017		59.3
Balance at Dec. 31, 2017	$ 1,241.2	$ 0.6	$ 112.7	$ 1,489.3	$ (362.8)	$ 1.4