Equity (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Preferred stock
Preferred stock, shares authorized	10.0				10.0				10.0	10.0
Computation of basic and diluted earnings per share
Net income attributable to DST Systems, Inc.	$ 37.9	$ 85.9	$ 144.9	$ 55.3	$ 39.2	$ 35.3	$ 55.2	$ 53.4	$ 324.0	$ 183.1	$ 318.5
Average common shares outstanding	45.0	45.1	45.0	44.5	44.1	45.8	46.5	46.4	44.9	45.7	46.9
Incremental shares from restricted stock units, stock options and convertible debentures									0.9	0.6	0.4
Average diluted shares outstanding	46.1	46.0	45.7	45.2	44.7	46.4	47.2	47.0	45.8	46.3	47.3
Basic earnings per share (in dollars per share)	$ 0.84	$ 1.90	$ 3.22	$ 1.24	$ 0.89	$ 0.77	$ 1.19	$ 1.15	$ 7.22	$ 4.01	$ 6.78
Diluted earnings per share (in dollars per share)	$ 0.82	$ 1.87	$ 3.17	$ 1.22	$ 0.88	$ 0.76	$ 1.17	$ 1.14	$ 7.08	$ 3.95	$ 6.73
Shares outstanding	44.3				44.1				44.3	44.1
Shares from options to purchase common stock, excluded from diluted earnings per share calculation									0.6	0.9
Number of shares of common stock issuable upon conversion of Series C debentures									1.8
Incremental shares from conversion spread on Series C debentures, when dilutive									0.1
Series A Preferred Stock
Preferred stock
Preferred stock, shares authorized	0.1								0.1
Fraction of newly issued share of Series A Preferred Stock (or in some cases, shares of the Company's common stock, other securities, cash or other assets) that could be purchased, for each Right									0.001
Purchase price (in dollars per share)	$ 225								$ 225