Debt (Details 2) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2012 Minimum	Jun. 30, 2012 Maximum	Jun. 30, 2012 Senior unsecured notes, 6.625% due May 2013	Jun. 30, 2011 Senior unsecured notes, 6.625% due May 2013	Jun. 30, 2012 Medium-term notes, Series B at 6.74% to 7.10% due from April 2013 to May 2018	Jun. 30, 2011 Medium-term notes, Series B at 6.74% to 7.10% due from April 2013 to May 2018	Jun. 30, 2012 Medium-term notes, Series B at 6.74% to 7.10% due from April 2013 to May 2018 Minimum	Jun. 30, 2011 Medium-term notes, Series B at 6.74% to 7.10% due from April 2013 to May 2018 Minimum	Jun. 30, 2012 Medium-term notes, Series B at 6.74% to 7.10% due from April 2013 to May 2018 Maximum	Jun. 30, 2011 Medium-term notes, Series B at 6.74% to 7.10% due from April 2013 to May 2018 Maximum	Jun. 30, 2012 Medium-term notes, Series C at 7.625% due August 2011	Jun. 30, 2011 Medium-term notes, Series C at 7.625% due August 2011	Jun. 28, 2011 Medium-term notes, Series C at 7.625% due August 2011	Jun. 30, 2012 Senior unsecured notes, 5.200% due July 2021	Jun. 30, 2011 Senior unsecured notes, 5.200% due July 2021	Jun. 28, 2011 Senior unsecured notes, 5.200% due July 2021
Long-term debt outstanding
Face amount						$ 100.0	$ 100.0	$ 56.0	$ 56.0						$ 100.0		$ 250.0	$ 250.0	$ 250.0
Interest rate (as a percent)						6.625%	6.625%			6.74%	6.74%	7.10%	7.10%	7.625%	7.625%	7.625%	5.20%	5.20%	5.20%
Total	406.9	507.8				101.3	102.4	56.0	56.0						99.8		249.6	249.6
Less amounts due within one year	101.0	100.0
Long-term debt, net of current portion	305.9	407.8
Fair value adjustments for interest rate swap contracts included in debt instrument carrying value	0.2	0.4
Remaining term of notes				1 year	3 years
Aggregate maturities of long-term debt, 2013	101.0
Aggregate maturities of long-term debt, 2014	0
Aggregate maturities of long-term debt, 2015	0
Aggregate maturities of long-term debt, 2016	0
Aggregate maturities of long-term debt, 2017	0
Aggregate maturities of long-term debt, thereafter	305.0
Interest costs	25.0	17.6	18.8
Interest costs, capitalized	$ 1.2	$ 0.5	$ 1.0