Condensed Consolidating Statements of Cash Flows (Details) (USD $) In Millions, unless otherwise specified	9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013
Operating activities:
Net cash provided	$ 681.8	$ 572.5
Investing activities:
Capital expenditures	(403.5)	(381.8)
Purchase or replacement of equipment under operating leases	(302.2)	(155.1)
Property investments in MSLLC	(25.6)	(25.0)
Proceeds from repayment of loans to affiliates		0
Loans to affiliates		0
Other investing activities	8.5	(1.9)
Net cash used for investing activities	(722.8)	(563.8)
Financing activities:
Proceeds from commercial paper	11,502.7	0
Repayment of commercial paper	(11,191.8)	0
Proceeds from issuance of long-term debt	175.0	1,468.7
Repayment of long-term debt	(502.8)	(1,301.8)
Debt costs	(4.4)	(109.3)
Dividends paid	(85.7)	(47.6)
Proceeds from loans from affiliates		0
Repayment of loans from affiliates		0
Other financing activities	(0.1)	4.6
Net cash provided by (used for) financing activities	(102.7)	14.6
Cash and cash equivalents:
Net increase (decrease) during each period	(143.7)	23.3
At beginning of year	429.5	72.6
At end of period	285.8	95.9
Parent [Member]
Operating activities:
Net cash provided	83.7	67.3
Investing activities:
Capital expenditures	0	0
Purchase or replacement of equipment under operating leases	0	0
Property investments in MSLLC	0	0
Proceeds from repayment of loans to affiliates		0
Loans to affiliates		0
Other investing activities	(1.2)	(0.7)
Net cash used for investing activities	(1.2)	(0.7)
Financing activities:
Proceeds from commercial paper	0
Repayment of commercial paper	0
Proceeds from issuance of long-term debt	0	0
Repayment of long-term debt	0	0
Debt costs		0
Dividends paid	(85.7)	(47.6)
Proceeds from loans from affiliates		0
Repayment of loans from affiliates		0
Other financing activities	4.3	4.6
Net cash provided by (used for) financing activities	(81.4)	(43.0)
Cash and cash equivalents:
Net increase (decrease) during each period	1.1	23.6
At beginning of year	0.4	0.1
At end of period	1.5	23.7
KCSR [Member]
Operating activities:
Net cash provided	241.9	187.2
Investing activities:
Capital expenditures	(270.1)	(246.6)
Purchase or replacement of equipment under operating leases	(203.8)	(88.6)
Property investments in MSLLC	0	0
Proceeds from repayment of loans to affiliates		97.4
Loans to affiliates		(69.5)
Other investing activities	9.0	(5.3)
Net cash used for investing activities	(464.9)	(312.6)
Financing activities:
Proceeds from commercial paper	11,502.7
Repayment of commercial paper	(11,191.8)
Proceeds from issuance of long-term debt	175.0	487.9
Repayment of long-term debt	(422.7)	(336.5)
Debt costs		(5.6)
Dividends paid	0	0
Proceeds from loans from affiliates		0
Repayment of loans from affiliates		0
Other financing activities	(1.2)	0
Net cash provided by (used for) financing activities	62.0	145.8
Cash and cash equivalents:
Net increase (decrease) during each period	(161.0)	20.4
At beginning of year	196.1	29.6
At end of period	35.1	50.0
Guarantor Subsidiaries [Member]
Operating activities:
Net cash provided	0.8	2.3
Investing activities:
Capital expenditures	(0.8)	(1.9)
Purchase or replacement of equipment under operating leases	0	0
Property investments in MSLLC	0	0
Proceeds from repayment of loans to affiliates		0
Loans to affiliates		0
Other investing activities	(1.0)	(1.0)
Net cash used for investing activities	(1.8)	(2.9)
Financing activities:
Proceeds from commercial paper	0
Repayment of commercial paper	0
Proceeds from issuance of long-term debt	0	0
Repayment of long-term debt	(0.1)	(0.1)
Debt costs		0
Dividends paid	0	0
Proceeds from loans from affiliates		0
Repayment of loans from affiliates		0
Other financing activities	1.0	0.6
Net cash provided by (used for) financing activities	0.9	0.5
Cash and cash equivalents:
Net increase (decrease) during each period	(0.1)	(0.1)
At beginning of year	0.2	0.1
At end of period	0.1	0
Non-Guarantor Subsidiaries [Member]
Operating activities:
Net cash provided	361.4	320.7
Investing activities:
Capital expenditures	(134.1)	(133.7)
Purchase or replacement of equipment under operating leases	(98.4)	(66.5)
Property investments in MSLLC	(25.6)	(25.0)
Proceeds from repayment of loans to affiliates		0
Loans to affiliates		0
Other investing activities	1.0	4.2
Net cash used for investing activities	(257.1)	(221.0)
Financing activities:
Proceeds from commercial paper	0
Repayment of commercial paper	0
Proceeds from issuance of long-term debt	0	980.8
Repayment of long-term debt	(80.0)	(965.2)
Debt costs		(103.7)
Dividends paid	(6.0)	(5.0)
Proceeds from loans from affiliates		69.5
Repayment of loans from affiliates		(97.4)
Other financing activities	(2.0)	0.7
Net cash provided by (used for) financing activities	(88.0)	(120.3)
Cash and cash equivalents:
Net increase (decrease) during each period	16.3	(20.6)
At beginning of year	232.8	42.8
At end of period	249.1	22.2
Consolidating Adjustments [Member]
Operating activities:
Net cash provided	(6.0)	(5.0)
Investing activities:
Capital expenditures	1.5	0.4
Purchase or replacement of equipment under operating leases	0	0
Property investments in MSLLC	0	0
Proceeds from repayment of loans to affiliates		(97.4)
Loans to affiliates		69.5
Other investing activities	0.7	0.9
Net cash used for investing activities	2.2	(26.6)
Financing activities:
Proceeds from commercial paper	0
Repayment of commercial paper	0
Proceeds from issuance of long-term debt	0	0
Repayment of long-term debt	0	0
Debt costs		0
Dividends paid	6.0	5.0
Proceeds from loans from affiliates		(69.5)
Repayment of loans from affiliates		97.4
Other financing activities	(2.2)	(1.3)
Net cash provided by (used for) financing activities	3.8	31.6
Cash and cash equivalents:
Net increase (decrease) during each period	0	0
At beginning of year	0	0
At end of period	$ 0	$ 0