Condensed Consolidating Statements of Cash Flows (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Operating activities:
Net cash provided	$ 143.3	$ 125.6
Investing activities:
Capital expenditures	(98.0)	(112.7)
Purchase of equipment under operating leases	(128.0)	0
Property investments in MSLLC	(19.6)	(12.9)
Proceeds from repayment of loans to affiliates		0
Other investing activities	5.7	2.8
Net cash used for investing activities	(239.9)	(122.8)
Financing activities:
Proceeds from commercial paper	864.6	0
Repayment of commercial paper	(689.8)	0
Proceeds from issuance of long-term debt	175.0	0
Repayment of long-term debt	(490.4)	(14.5)
Dividends paid	(23.8)	0
Repayment of loans from affiliates		0
Other financing activities	(1.0)	2.8
Net cash used for financing activities	(165.4)	(11.7)
Cash and cash equivalents:
Net decrease during each period	(262.0)	(8.9)
At beginning of year	429.5	72.6
At end of period	167.5	63.7
Parent [Member]
Operating activities:
Net cash provided	21.3	(3.0)
Investing activities:
Capital expenditures	0	0
Purchase of equipment under operating leases	0
Property investments in MSLLC	0	0
Proceeds from repayment of loans to affiliates		0
Other investing activities	(0.2)	(0.4)
Net cash used for investing activities	(0.2)	(0.4)
Financing activities:
Proceeds from commercial paper	0
Repayment of commercial paper	0
Proceeds from issuance of long-term debt	0
Repayment of long-term debt	0	0
Dividends paid	(23.8)
Repayment of loans from affiliates		0
Other financing activities	2.6	3.3
Net cash used for financing activities	(21.2)	3.3
Cash and cash equivalents:
Net decrease during each period	(0.1)	(0.1)
At beginning of year	0.4	0.1
At end of period	0.3	0
KCSR [Member]
Operating activities:
Net cash provided	15.9	(1.6)
Investing activities:
Capital expenditures	(59.2)	(76.2)
Purchase of equipment under operating leases	(42.9)
Property investments in MSLLC	0	0
Proceeds from repayment of loans to affiliates		59.4
Other investing activities	0.6	1.8
Net cash used for investing activities	(101.5)	(15.0)
Financing activities:
Proceeds from commercial paper	864.6
Repayment of commercial paper	(689.8)
Proceeds from issuance of long-term debt	175.0
Repayment of long-term debt	(421.1)	(8.2)
Dividends paid	0
Repayment of loans from affiliates		0
Other financing activities	(0.8)	(0.4)
Net cash used for financing activities	(72.1)	(8.6)
Cash and cash equivalents:
Net decrease during each period	(157.7)	(25.2)
At beginning of year	196.1	29.6
At end of period	38.4	4.4
Guarantor Subsidiaries [Member]
Operating activities:
Net cash provided	0.4	0.8
Investing activities:
Capital expenditures	(0.4)	(0.8)
Purchase of equipment under operating leases	0
Property investments in MSLLC	0	0
Proceeds from repayment of loans to affiliates		0
Other investing activities	(0.2)	(0.3)
Net cash used for investing activities	(0.6)	(1.1)
Financing activities:
Proceeds from commercial paper	0
Repayment of commercial paper	0
Proceeds from issuance of long-term debt	0
Repayment of long-term debt	(0.1)	(0.1)
Dividends paid	0
Repayment of loans from affiliates		0
Other financing activities	0.2	0.3
Net cash used for financing activities	0.1	0.2
Cash and cash equivalents:
Net 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	105.7	129.4
Investing activities:
Capital expenditures	(39.9)	(35.7)
Purchase of equipment under operating leases	(85.1)
Property investments in MSLLC	(19.6)	(12.9)
Proceeds from repayment of loans to affiliates		0
Other investing activities	6.6	1.0
Net cash used for investing activities	(138.0)	(47.6)
Financing activities:
Proceeds from commercial paper	0
Repayment of commercial paper	0
Proceeds from issuance of long-term debt	0
Repayment of long-term debt	(69.2)	(6.2)
Dividends paid	0
Repayment of loans from affiliates		(59.4)
Other financing activities	(2.6)	0.3
Net cash used for financing activities	(71.8)	(65.3)
Cash and cash equivalents:
Net decrease during each period	(104.1)	16.5
At beginning of year	232.8	42.8
At end of period	128.7	59.3
Consolidating Adjustments [Member]
Operating activities:
Net cash provided	0	0
Investing activities:
Capital expenditures	1.5	0
Purchase of equipment under operating leases	0
Property investments in MSLLC	0	0
Proceeds from repayment of loans to affiliates		(59.4)
Other investing activities	(1.1)	0.7
Net cash used for investing activities	0.4	(58.7)
Financing activities:
Proceeds from commercial paper	0
Repayment of commercial paper	0
Proceeds from issuance of long-term debt	0
Repayment of long-term debt	0	0
Dividends paid	0
Repayment of loans from affiliates		59.4
Other financing activities	(0.4)	(0.7)
Net cash used for financing activities	(0.4)	58.7
Cash and cash equivalents:
Net decrease during each period	0	0
At beginning of year	0	0
At end of period	$ 0	$ 0