Condensed Consolidating Statements of Cash Flows (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
Operating activities:
Net cash provided	$ 733.7	$ 683.6
Investing activities:
Capital expenditures	(446.9)	(405.1)
Purchase or replacement of equipment under operating leases	(42.6)	(26.6)
Property investments in MSLLC	(23.7)	(31.2)
Investments in and advances to affiliates	(20.3)	(0.9)
Proceeds from repayment of loans to affiliates	0.0	0.0
Loans to affiliates	0.0	0.0
Proceeds from disposal of property	6.6	3.6
Other investing activities	(15.1)	(5.8)
Net cash provided (used)	(542.0)	(466.0)
Financing activities:
Proceeds from short-term borrowings	9,772.2	6,499.0
Repayment of short-term borrowings	(9,600.9)	(6,579.3)
Proceeds from issuance of long-term debt	0.0	248.7
Repayment of long-term debt	(20.2)	(20.8)
Dividends paid	(105.1)	(107.2)
Shares repurchased	(320.4)	(99.8)
Proceeds from loans from affiliates	0.0	0.0
Repayment of loans from affiliates	0.0	0.0
Contribution from affiliates	0.0	0.0
Other financing activities	0.5	(1.7)
Net cash used for financing activities	(273.9)	(61.1)
Cash and cash equivalents:
Net increase (decrease) during each period	(82.2)	156.5
At beginning of year	170.6	136.6
At end of period	88.4	293.1
Condensed Consolidating Financial Information KCS [Member] | Consolidating Adjustments [Member]
Operating activities:
Net cash provided	(5.0)	(163.9)
Investing activities:
Capital expenditures	0.0	0.0
Purchase or replacement of equipment under operating leases	0.0	0.0
Property investments in MSLLC	0.0	0.0
Investments in and advances to affiliates	1.0	109.9
Proceeds from repayment of loans to affiliates	(9,814.6)	(6,743.5)
Loans to affiliates	9,772.2	6,742.5
Proceeds from disposal of property	0.0	(0.1)
Other investing activities	0.0	0.1
Net cash provided (used)	(41.4)	108.9
Financing activities:
Proceeds from short-term borrowings	0.0	(243.5)
Repayment of short-term borrowings	0.0	0.0
Proceeds from issuance of long-term debt		0.0
Repayment of long-term debt	0.0	0.0
Dividends paid	5.0	162.2
Shares repurchased	0.0	0.0
Proceeds from loans from affiliates	(9,772.2)	(6,499.0)
Repayment of loans from affiliates	9,814.6	6,743.5
Contribution from affiliates	(1.0)	(109.9)
Other financing activities	0.0	1.7
Net cash used for financing activities	46.4	55.0
Cash and cash equivalents:
Net increase (decrease) during each period	0.0	0.0
At beginning of year	0.0	0.0
At end of period	0.0	0.0
Condensed Consolidating Financial Information KCS [Member] | Parent [Member]
Operating activities:
Net cash provided	215.1	178.2
Investing activities:
Capital expenditures	0.0	0.0
Purchase or replacement of equipment under operating leases	0.0	0.0
Property investments in MSLLC	0.0	0.0
Investments in and advances to affiliates	(0.5)	(103.4)
Proceeds from repayment of loans to affiliates	9,814.6	6,743.5
Loans to affiliates	(9,772.2)	(6,742.5)
Proceeds from disposal of property	0.0	0.0
Other investing activities	0.0	0.0
Net cash provided (used)	41.9	(102.4)
Financing activities:
Proceeds from short-term borrowings	9,772.2	6,499.0
Repayment of short-term borrowings	(9,600.9)	(6,579.3)
Proceeds from issuance of long-term debt		248.7
Repayment of long-term debt	0.0	0.0
Dividends paid	(105.1)	(107.2)
Shares repurchased	(320.4)	(99.8)
Proceeds from loans from affiliates	0.0	0.0
Repayment of loans from affiliates	0.0	0.0
Contribution from affiliates	0.0	0.0
Other financing activities	0.5	(1.5)
Net cash used for financing activities	(253.7)	(40.1)
Cash and cash equivalents:
Net increase (decrease) during each period	3.3	35.7
At beginning of year	0.2	0.2
At end of period	3.5	35.9
Condensed Consolidating Financial Information KCS [Member] | Guarantor Subsidiaries [Member]
Operating activities:
Net cash provided	413.9	380.8
Investing activities:
Capital expenditures	(292.9)	(269.5)
Purchase or replacement of equipment under operating leases	(42.6)	(26.6)
Property investments in MSLLC	0.0	0.0
Investments in and advances to affiliates	(0.5)	(6.5)
Proceeds from repayment of loans to affiliates	0.0	0.0
Loans to affiliates	0.0	0.0
Proceeds from disposal of property	5.2	1.4
Other investing activities	(16.5)	(10.4)
Net cash provided (used)	(347.3)	(311.6)
Financing activities:
Proceeds from short-term borrowings	0.0	243.5
Repayment of short-term borrowings	0.0	0.0
Proceeds from issuance of long-term debt		0.0
Repayment of long-term debt	(2.7)	(2.6)
Dividends paid	0.0	0.0
Shares repurchased	0.0	0.0
Proceeds from loans from affiliates	9,772.2	6,499.0
Repayment of loans from affiliates	(9,814.6)	(6,743.5)
Contribution from affiliates	0.5	103.1
Other financing activities	0.0	(0.1)
Net cash used for financing activities	(44.6)	99.4
Cash and cash equivalents:
Net increase (decrease) during each period	22.0	168.6
At beginning of year	32.6	10.2
At end of period	54.6	178.8
Condensed Consolidating Financial Information KCS [Member] | Non-Guarantor Subsidiaries [Member]
Operating activities:
Net cash provided	109.7	288.5
Investing activities:
Capital expenditures	(154.0)	(135.6)
Purchase or replacement of equipment under operating leases	0.0	0.0
Property investments in MSLLC	(23.7)	(31.2)
Investments in and advances to affiliates	(20.3)	(0.9)
Proceeds from repayment of loans to affiliates	0.0	0.0
Loans to affiliates	0.0	0.0
Proceeds from disposal of property	1.4	2.3
Other investing activities	1.4	4.5
Net cash provided (used)	(195.2)	(160.9)
Financing activities:
Proceeds from short-term borrowings	0.0	0.0
Repayment of short-term borrowings	0.0	0.0
Proceeds from issuance of long-term debt		0.0
Repayment of long-term debt	(17.5)	(18.2)
Dividends paid	(5.0)	(162.2)
Shares repurchased	0.0	0.0
Proceeds from loans from affiliates	0.0	0.0
Repayment of loans from affiliates	0.0	0.0
Contribution from affiliates	0.5	6.8
Other financing activities	0.0	(1.8)
Net cash used for financing activities	(22.0)	(175.4)
Cash and cash equivalents:
Net increase (decrease) during each period	(107.5)	(47.8)
At beginning of year	137.8	126.2
At end of period	30.3	78.4
Condensed Consolidating Financial Information KCSR [Member] | Consolidating Adjustments [Member]
Operating activities:
Net cash provided	(5.0)	(163.9)
Investing activities:
Capital expenditures	0.0	0.0
Purchase or replacement of equipment under operating leases	0.0	0.0
Property investments in MSLLC	0.0	0.0
Investments in and advances to affiliates	1.0	109.9
Proceeds from repayment of loans to affiliates	(9,814.6)	(6,743.5)
Loans to affiliates	9,772.2	6,742.5
Proceeds from disposal of property	0.0	(0.1)
Other investing activities	0.0	0.1
Net cash provided (used)	(41.4)	108.9
Financing activities:
Proceeds from short-term borrowings	0.0	(243.5)
Repayment of short-term borrowings	0.0	0.0
Proceeds from issuance of long-term debt		0.0
Repayment of long-term debt	0.0	0.0
Dividends paid	5.0	162.2
Shares repurchased	0.0	0.0
Proceeds from loans from affiliates	(9,772.2)	(6,499.0)
Repayment of loans from affiliates	9,814.6	6,743.5
Contribution from affiliates	(1.0)	(109.9)
Other financing activities	0.0	1.7
Net cash used for financing activities	46.4	55.0
Cash and cash equivalents:
Net increase (decrease) during each period	0.0	0.0
At beginning of year	0.0	0.0
At end of period	0.0	0.0
Condensed Consolidating Financial Information KCSR [Member] | Parent [Member]
Operating activities:
Net cash provided	215.1	178.2
Investing activities:
Capital expenditures	0.0	0.0
Purchase or replacement of equipment under operating leases	0.0	0.0
Property investments in MSLLC	0.0	0.0
Investments in and advances to affiliates	(0.5)	(103.4)
Proceeds from repayment of loans to affiliates	9,814.6	6,743.5
Loans to affiliates	(9,772.2)	(6,742.5)
Proceeds from disposal of property	0.0	0.0
Other investing activities	0.0	0.0
Net cash provided (used)	41.9	(102.4)
Financing activities:
Proceeds from short-term borrowings	9,772.2	6,499.0
Repayment of short-term borrowings	(9,600.9)	(6,579.3)
Proceeds from issuance of long-term debt		248.7
Repayment of long-term debt	0.0	0.0
Dividends paid	(105.1)	(107.2)
Shares repurchased	(320.4)	(99.8)
Proceeds from loans from affiliates	0.0	0.0
Repayment of loans from affiliates	0.0	0.0
Contribution from affiliates	0.0	0.0
Other financing activities	0.5	(1.5)
Net cash used for financing activities	(253.7)	(40.1)
Cash and cash equivalents:
Net increase (decrease) during each period	3.3	35.7
At beginning of year	0.2	0.2
At end of period	3.5	35.9
Condensed Consolidating Financial Information KCSR [Member] | KCSR [Member]
Operating activities:
Net cash provided	413.5	380.2
Investing activities:
Capital expenditures	(292.6)	(269.0)
Purchase or replacement of equipment under operating leases	(42.6)	(26.6)
Property investments in MSLLC	0.0	0.0
Investments in and advances to affiliates	0.0	0.0
Proceeds from repayment of loans to affiliates	0.0	0.0
Loans to affiliates	0.0	0.0
Proceeds from disposal of property	5.2	1.4
Other investing activities	(16.5)	(10.4)
Net cash provided (used)	(346.5)	(304.6)
Financing activities:
Proceeds from short-term borrowings	0.0	243.5
Repayment of short-term borrowings	0.0	0.0
Proceeds from issuance of long-term debt		0.0
Repayment of long-term debt	(2.6)	(2.5)
Dividends paid	0.0	0.0
Shares repurchased	0.0	0.0
Proceeds from loans from affiliates	9,772.2	6,499.0
Repayment of loans from affiliates	(9,814.6)	(6,743.5)
Contribution from affiliates	0.0	96.6
Other financing activities	0.0	(0.1)
Net cash used for financing activities	(45.0)	93.0
Cash and cash equivalents:
Net increase (decrease) during each period	22.0	168.6
At beginning of year	32.6	10.1
At end of period	54.6	178.7
Condensed Consolidating Financial Information KCSR [Member] | Guarantor Subsidiaries [Member]
Operating activities:
Net cash provided	0.4	0.6
Investing activities:
Capital expenditures	(0.3)	(0.5)
Purchase or replacement of equipment under operating leases	0.0	0.0
Property investments in MSLLC	0.0	0.0
Investments in and advances to affiliates	(0.5)	(6.5)
Proceeds from repayment of loans to affiliates	0.0	0.0
Loans to affiliates	0.0	0.0
Proceeds from disposal of property	0.0	0.0
Other investing activities	0.0	0.0
Net cash provided (used)	(0.8)	(7.0)
Financing activities:
Proceeds from short-term borrowings	0.0	0.0
Repayment of short-term borrowings	0.0	0.0
Proceeds from issuance of long-term debt		0.0
Repayment of long-term debt	(0.1)	(0.1)
Dividends paid	0.0	0.0
Shares repurchased	0.0	0.0
Proceeds from loans from affiliates	0.0	0.0
Repayment of loans from affiliates	0.0	0.0
Contribution from affiliates	0.5	6.5
Other financing activities	0.0	0.0
Net cash used for financing activities	0.4	6.4
Cash and cash equivalents:
Net increase (decrease) during each period	0.0	0.0
At beginning of year	0.0	0.1
At end of period	0.0	0.1
Condensed Consolidating Financial Information KCSR [Member] | Non-Guarantor Subsidiaries [Member]
Operating activities:
Net cash provided	109.7	288.5
Investing activities:
Capital expenditures	(154.0)	(135.6)
Purchase or replacement of equipment under operating leases	0.0	0.0
Property investments in MSLLC	(23.7)	(31.2)
Investments in and advances to affiliates	(20.3)	(0.9)
Proceeds from repayment of loans to affiliates	0.0	0.0
Loans to affiliates	0.0	0.0
Proceeds from disposal of property	1.4	2.3
Other investing activities	1.4	4.5
Net cash provided (used)	(195.2)	(160.9)
Financing activities:
Proceeds from short-term borrowings	0.0	0.0
Repayment of short-term borrowings	0.0	0.0
Proceeds from issuance of long-term debt		0.0
Repayment of long-term debt	(17.5)	(18.2)
Dividends paid	(5.0)	(162.2)
Shares repurchased	0.0	0.0
Proceeds from loans from affiliates	0.0	0.0
Repayment of loans from affiliates	0.0	0.0
Contribution from affiliates	0.5	6.8
Other financing activities	0.0	(1.8)
Net cash used for financing activities	(22.0)	(175.4)
Cash and cash equivalents:
Net increase (decrease) during each period	(107.5)	(47.8)
At beginning of year	137.8	126.2
At end of period	$ 30.3	$ 78.4