Quarterly Financial Data (Unaudited) (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
Quarterly Financial Data (Unaudited)
Operating revenues	$ 487.0	$ 464.0	$ 465.5	$ 475.9	$ 457.3	$ 433.1	$ 424.1	$ 429.5	$ 1,892.4	$ 1,744.0	$ 1,713.6
Out-of-pocket reimbursements	171.6	168.0	167.3	177.3	166.1	158.3	158.1	162.2	684.2	644.7	614.9
Total revenues (includes related party revenues of $183.4, $192.0 and $202.6)	658.6	632.0	632.8	653.2	623.4	591.4	582.2	591.7	2,576.6	2,388.7	2,328.5
Costs and expenses	559.8	544.4	539.6	559.1	530.6	496.5	477.6	492.3	2,202.9	1,997.0	1,848.5
Depreciation and amortization (including goodwill impairment)	99.6	40.5	42.3	34.0	36.5	33.7	31.3	30.1	216.4	131.6	135.4
Income from operations	(0.8)	47.1	50.9	60.1	56.3	61.2	73.3	69.3	157.3	260.1	344.6
Interest expense	(9.5)	(10.6)	(11.7)	(11.7)	(11.9)	(10.9)	(12.0)	(11.7)	(43.5)	(46.5)	(46.1)
Other income (expense), net	77.2	72.4	194.2	29.7	11.4	(4.5)	14.6	17.2	373.5	38.7	141.7
Equity in earnings of unconsolidated affiliates	22.4	3.1	1.4	5.3	4.4	1.7	7.2	8.4	32.2	21.7	36.4
Income before income taxes and non-controlling interest	89.3	112.0	234.8	83.4	60.2	47.5	83.1	83.2	519.5	274.0	476.6
Income taxes	51.4	26.1	89.9	28.1	23.0	14.0	28.7	30.1	195.5	95.8	159.1
Net income	37.9	85.9	144.9	55.3	37.2	33.5	54.4	53.1	324.0	178.2	317.5
Net loss attributable to non-controlling interests					2.0	1.8	0.8	0.3		4.9	1.0
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 (in shares)	45.0	45.1	45.0	44.5	44.1	45.8	46.5	46.4	44.9	45.7	46.9
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
Average diluted shares outstanding (in shares)	46.1	46.0	45.7	45.2	44.7	46.4	47.2	47.0	45.8	46.3	47.3
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
Cash dividends per share of common stock (in dollars per share)	$ 0.40			$ 0.40		$ 0.35		$ 0.35	$ 0.80	$ 0.70	$ 0.60