Quarterly Financial Data (Unaudited) (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2011
Quarterly Financial Data (Unaudited)
Net sales	$ 611.8	$ 581.4	$ 533.5	$ 544.9	$ 643.7	$ 539.9	$ 431.1	$ 414.1	$ 2,271.7	$ 2,028.7	$ 1,675.1
Gross profit	120.5	101.0	102.6	109.3	120.6	105.1	84.3	81.1	433.5	391.0	249.0
Operating income	65.4	53.0	52.7	61.6	66.5	55.7	43.9	44.0	232.7	210.1	96.4
Net income	40.9	32.9	33.2	39.5	41.0	33.0	23.8	23.7	146.5	121.6	71.7
Net income attributable to Carpenter	$ 40.9	$ 32.9	$ 33.0	$ 39.2	$ 40.8	$ 33.0	$ 23.6	$ 23.8	$ 146.1	$ 121.2	$ 71.0
Basic (in dollars per share)	$ 0.77	$ 0.62	$ 0.62	$ 0.74	$ 0.77	$ 0.69	$ 0.53	$ 0.53	$ 2.75	$ 2.55	$ 1.59
Diluted (in dollars per share)	$ 0.77	$ 0.62	$ 0.62	$ 0.74	$ 0.77	$ 0.69	$ 0.52	$ 0.53	$ 2.73	$ 2.53	$ 1.59
Weighted average common shares outstanding, basic	52.9	52.9	52.9	52.8	52.6	47.2	44.4	44.3	52.9	47.1	44.1
Weighted average common shares outstanding, diluted	53.5	53.5	53.5	53.4	53.3	47.9	45.1	45.1	53.4	47.8	44.7