Employee Benefit Plans (Details 2) (Defined Benefit Pension Plans, USD $) In Millions, unless otherwise specified																							12 Months Ended
	May 31, 2013	May 31, 2012	May 31, 2011	May 31, 2013 Quoted prices in active markets (Level 1)	May 31, 2012 Quoted prices in active markets (Level 1)	May 31, 2013 Quoted prices in active markets (Level 1) U.S. common stock	May 31, 2012 Quoted prices in active markets (Level 1) U.S. common stock	May 31, 2013 Quoted prices in active markets (Level 1) U.S. mutual funds	May 31, 2012 Quoted prices in active markets (Level 1) U.S. mutual funds	May 31, 2013 Quoted prices in active markets (Level 1) International common stock	May 31, 2012 Quoted prices in active markets (Level 1) International common stock	May 31, 2013 Quoted prices in active markets (Level 1) International mutual funds	May 31, 2012 Quoted prices in active markets (Level 1) International mutual funds	May 31, 2013 Quoted prices in active markets (Level 1) Government securities mutual funds	May 31, 2012 Quoted prices in active markets (Level 1) Government securities mutual funds	May 31, 2013 Quoted prices in active markets (Level 1) Corporate bonds mutual funds	May 31, 2013 Quoted prices in active markets (Level 1) Cash and cash equivalents	May 31, 2012 Quoted prices in active markets (Level 1) Cash and cash equivalents	May 31, 2013 Significant other observable inputs (Level 2)	May 31, 2012 Significant other observable inputs (Level 2)	May 31, 2013 Significant other observable inputs (Level 2) Hedge fund-of-funds	May 31, 2012 Significant other observable inputs (Level 2) Hedge fund-of-funds	May 31, 2013 Significant other unobservable inputs (Level 3)	May 31, 2013 Significant other unobservable inputs (Level 3) Hedge funds	May 31, 2013 Significant other unobservable inputs (Level 3) Hedge fund-of-funds	May 31, 2013 Total	May 31, 2012 Total	May 31, 2013 Total U.S. common stock	May 31, 2012 Total U.S. common stock	May 31, 2013 Total U.S. mutual funds	May 31, 2012 Total U.S. mutual funds	May 31, 2013 Total International common stock	May 31, 2012 Total International common stock	May 31, 2013 Total International mutual funds	May 31, 2012 Total International mutual funds	May 31, 2013 Total Government securities mutual funds	May 31, 2012 Total Government securities mutual funds	May 31, 2013 Total Corporate bonds mutual funds	May 31, 2013 Total Hedge funds	May 31, 2012 Total Hedge funds	May 31, 2013 Total Hedge fund-of-funds	May 31, 2012 Total Hedge fund-of-funds	May 31, 2013 Total Cash and cash equivalents	May 31, 2012 Total Cash and cash equivalents
Employee benefit plans
Fair value of plan assets	$ 101.6	$ 87.7	$ 94.4	$ 47.4	$ 40.8	$ 6.1	$ 3.4	$ 21.7	$ 19.6	$ 0.7	$ 0.8	$ 6.7	$ 5.5	$ 7.2	$ 11.4	$ 4.0	$ 1.0	$ 0.1	$ 44.1	$ 37.5	$ 44.1	$ 37.5	$ 10.1	$ 2.4	$ 7.7	$ 101.6	$ 87.7	$ 6.1	$ 3.4	$ 21.7	$ 19.6	$ 0.7	$ 0.8	$ 6.7	$ 5.5	$ 7.2	$ 11.4	$ 4.0	$ 2.4	$ 2.3	$ 51.8	$ 44.6	$ 1.0	$ 0.1
Reconciliation of Level 3 pension assets measured at fair value
Fair value of plan assets at beginning of year	101.6	87.7	94.4	47.4	40.8	6.1	3.4	21.7	19.6	0.7	0.8	6.7	5.5	7.2	11.4	4.0	1.0	0.1	44.1	37.5	44.1	37.5	9.4	2.3	7.1	101.6	87.7	6.1	3.4	21.7	19.6	0.7	0.8	6.7	5.5	7.2	11.4	4.0	2.4	2.3	51.8	44.6	1.0	0.1
Actual return on plan assets:
Relating to assets still held at reporting date																							0.7	0.1	0.6
Fair value of plan assets at end of year	$ 101.6	$ 87.7	$ 94.4	$ 47.4	$ 40.8	$ 6.1	$ 3.4	$ 21.7	$ 19.6	$ 0.7	$ 0.8	$ 6.7	$ 5.5	$ 7.2	$ 11.4	$ 4.0	$ 1.0	$ 0.1	$ 44.1	$ 37.5	$ 44.1	$ 37.5	$ 10.1	$ 2.4	$ 7.7	$ 101.6	$ 87.7	$ 6.1	$ 3.4	$ 21.7	$ 19.6	$ 0.7	$ 0.8	$ 6.7	$ 5.5	$ 7.2	$ 11.4	$ 4.0	$ 2.4	$ 2.3	$ 51.8	$ 44.6	$ 1.0	$ 0.1