Condensed Consolidating Statements of Cash Flows (Details) (USD $) In Millions, unless otherwise specified	6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013
Operating activities:
Net cash provided	$ 396.3	$ 326.4
Investing activities:
Capital expenditures	(268.0)	(265.9)
Purchase or replacement of equipment under operating leases	(294.3)	(155.1)
Property investments in MSLLC	(24.8)	(22.6)
Proceeds from repayment of loans to affiliates		0
Loans to affiliates		0
Other investing activities	7.5	(0.6)
Net cash used for investing activities	(579.6)	(444.2)
Financing activities:
Proceeds from commercial paper	5,081.5	0
Repayment of commercial paper	(4,761.1)	0
Proceeds from issuance of long-term debt	175.0	1,403.7
Repayment of long-term debt	(495.4)	(1,203.2)
Debt costs	(4.1)	(105.7)
Dividends paid	(54.8)	(23.8)
Proceeds from loans from affiliates		0
Repayment of loans from affiliates		0
Other financing activities	(1.2)	4.2
Net cash provided by (used for) financing activities	(56.0)	75.2
Cash and cash equivalents:
Net decrease during each period	(239.3)	(42.6)
At beginning of year	429.5	72.6
At end of period	190.2	30.0
Parent [Member]
Operating activities:
Net cash provided	52.3	20.4
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	(0.7)	(0.5)
Net cash used for investing activities	(0.7)	(0.5)
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	(54.8)	(23.8)
Proceeds from loans from affiliates		0
Repayment of loans from affiliates		0
Other financing activities	2.9	4.2
Net cash provided by (used for) financing activities	(51.9)	(19.6)
Cash and cash equivalents:
Net decrease during each period	(0.3)	0.3
At beginning of year	0.4	0.1
At end of period	0.1	0.4
KCSR [Member]
Operating activities:
Net cash provided	106.9	95.1
Investing activities:
Capital expenditures	(180.3)	(179.5)
Purchase or replacement of equipment under operating leases	(196.1)	(88.6)
Property investments in MSLLC	0	0
Proceeds from repayment of loans to affiliates		59.4
Loans to affiliates		(52.5)
Other investing activities	8.5	(3.4)
Net cash used for investing activities	(367.9)	(264.6)
Financing activities:
Proceeds from commercial paper	5,081.5
Repayment of commercial paper	(4,761.1)
Proceeds from issuance of long-term debt	175.0	475.9
Repayment of long-term debt	(421.9)	(320.2)
Debt costs		(5.2)
Dividends paid	0	0
Proceeds from loans from affiliates		0
Repayment of loans from affiliates		0
Other financing activities	(1.0)	0
Net cash provided by (used for) financing activities	72.5	150.5
Cash and cash equivalents:
Net decrease during each period	(188.5)	(19.0)
At beginning of year	196.1	29.6
At end of period	7.6	10.6
Guarantor Subsidiaries [Member]
Operating activities:
Net cash provided	0.8	1.6
Investing activities:
Capital expenditures	(0.7)	(1.5)
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	(0.5)	(0.5)
Net cash used for investing activities	(1.2)	(2.0)
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	0.5	0.5
Net cash provided by (used for) financing activities	0.4	0.4
Cash and cash equivalents:
Net decrease during each period	0	0
At beginning of year	0.2	0.1
At end of period	0.2	0.1
Non-Guarantor Subsidiaries [Member]
Operating activities:
Net cash provided	242.3	214.3
Investing activities:
Capital expenditures	(88.5)	(85.2)
Purchase or replacement of equipment under operating leases	(98.2)	(66.5)
Property investments in MSLLC	(24.8)	(22.6)
Proceeds from repayment of loans to affiliates		0
Loans to affiliates		0
Other investing activities	0.5	3.1
Net cash used for investing activities	(211.0)	(171.2)
Financing activities:
Proceeds from commercial paper	0
Repayment of commercial paper	0
Proceeds from issuance of long-term debt	0	927.8
Repayment of long-term debt	(73.4)	(882.9)
Debt costs		(100.5)
Dividends paid	(6.0)	(5.0)
Proceeds from loans from affiliates		52.5
Repayment of loans from affiliates		(59.4)
Other financing activities	(2.4)	0.5
Net cash provided by (used for) financing activities	(81.8)	(67.0)
Cash and cash equivalents:
Net decrease during each period	(50.5)	(23.9)
At beginning of year	232.8	42.8
At end of period	182.3	18.9
Consolidating Adjustments [Member]
Operating activities:
Net cash provided	(6.0)	(5.0)
Investing activities:
Capital expenditures	1.5	0.3
Purchase or replacement of equipment under operating leases	0	0
Property investments in MSLLC	0	0
Proceeds from repayment of loans to affiliates		(59.4)
Loans to affiliates		52.5
Other investing activities	(0.3)	0.7
Net cash used for investing activities	1.2	(5.9)
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	0
Debt costs		0
Dividends paid	6.0	5.0
Proceeds from loans from affiliates		(52.5)
Repayment of loans from affiliates		59.4
Other financing activities	(1.2)	(1.0)
Net cash provided by (used for) financing activities	4.8	10.9
Cash and cash equivalents:
Net decrease during each period	0	0
At beginning of year	0	0
At end of period	$ 0	$ 0