Debt (Details) (USD $) In Millions, unless otherwise specified	6 Months Ended
	Dec. 31, 2011	Dec. 31, 2010
Line Of Credit Facility [Line Items]
Outstanding borrowings	$ 0	$ 0
Aggregate commitments including borrowings and letters of credit	400
Line of credit facility, annual fee, percentage	1.75%
Commitment fee percentage	0.20%
Revolving Credit Facility [Member]
Line Of Credit Facility [Line Items]
Increase in borrowings and letters of credit	550.0
Borrowings and letters of credit, maturity date	May 2016
Letter of credit, outstanding	9.3
Previous Revolving Credit Facility [Member]
Line Of Credit Facility [Line Items]
Aggregate commitments including borrowings and letters of credit	175
Borrowings and letters of credit, maturity date	January 2012
Letter of credit, outstanding		$ 4.6
Prime Rate [Member]
Line Of Credit Facility [Line Items]
Percentage of maximum raise in interest rate over base rate	1.50%
Prime Rate [Member] | Revolving Credit Facility [Member]
Line Of Credit Facility [Line Items]
Addition to LIBOR to determine interest rate	0.75%
LIBOR [Member]
Line Of Credit Facility [Line Items]
Percentage of maximum raise in interest rate over base rate	2.50%
LIBOR [Member] | Revolving Credit Facility [Member]
Line Of Credit Facility [Line Items]
Addition to LIBOR to determine interest rate	1.75%