Consolidated Statements of Comprehensive Income (Unaudited) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Statement of Comprehensive Income [Abstract]
Net income	$ 17.2	$ 9.1	$ 25.3	$ 18.9
Other comprehensive (loss) income:
Foreign currency translation adjustment	(0.3)	0.1	(0.5)	(0.1)
Less: Income tax (benefit) expense on foreign currency translation adjustment	(0.1)	0.1	(0.2)	0.0
Comprehensive income	17.0	9.1	25.0	18.8
Less: Comprehensive income attributable to noncontrolling interest	0.1	0.1	0.2	0.2
Comprehensive income (loss) attributable to Global Brass and Copper Holdings, Inc.	$ 16.9	$ 9.0	$ 24.8	$ 18.6