Long-Term Borrowings (Details) (USD $) In Millions	6 Months Ended
	Sep. 30, 2011	Mar. 31, 2011	Nov. 30, 2010
Long-Term Borrowings
Senior unsecured notes due 2018 (net of $1.2 million and $1.3 million of unamortized discount at September 30, 2011 and March 31, 2011, respectively)	$ 298.8	$ 298.7
Capital leases and other obligations	60.3	56.2
Total	359.1	354.9
Less current maturities of capital leases and other obligations (included in accrued liabilities)	(22.2)	(19.3)
Long-term borrowings	336.9	335.6
Long-Term Borrowings (Textuals) [Abstract]
Maximum amount of credit facility			600.0
Unamortized discount	1.2	1.3
Expiration date of credit facility	Nov. 30, 2014
Amount of unsecured revolving credit facility			400.0
Provision for swing line loans (maximum)			25.0
Provision for standby letters of credit (maximum)			$ 50.0
Period One [Member]
Debt Instrument [Line Items]
Interest periods for revolving loans under the credit facility	1 month
Period Two [Member]
Debt Instrument [Line Items]
Interest periods for revolving loans under the credit facility	2 months
Period Three [Member]
Debt Instrument [Line Items]
Interest periods for revolving loans under the credit facility	3 months
Period Four [Member]
Debt Instrument [Line Items]
Interest periods for revolving loans under the credit facility	6 months