Commitments and Contingencies - Summary of Environmental Reserve Activity (Detail) (USD $) In Millions, unless otherwise specified	9 Months Ended
	Aug. 31, 2013
Commitment And Contingencies [Line Items]
Environmental reserve, Beginning Balance	$ 189.5
Adjustments	10.7
Expenditures	(21.1)
Environmental reserve, Ending Balance	179.1
Aerojet - Sacramento [Member]
Commitment And Contingencies [Line Items]
Environmental reserve, Beginning Balance	140.5
Adjustments	5.4
Expenditures	(13.8)
Environmental reserve, Ending Balance	132.1
Aerojet - BPOU [Member]
Commitment And Contingencies [Line Items]
Environmental reserve, Beginning Balance	31.2
Adjustments	2.4
Expenditures	(5.0)
Environmental reserve, Ending Balance	28.6
Other Aerojet Sites [Member]
Commitment And Contingencies [Line Items]
Environmental reserve, Beginning Balance	10.8
Adjustments	(0.2)
Expenditures	(1.8)
Environmental reserve, Ending Balance	8.8
Total Aerojet [Member]
Commitment And Contingencies [Line Items]
Environmental reserve, Beginning Balance	182.5
Adjustments	7.6
Expenditures	(20.6)
Environmental reserve, Ending Balance	169.5
Other [Member]
Commitment And Contingencies [Line Items]
Environmental reserve, Beginning Balance	7.0
Adjustments	3.1
Expenditures	(0.5)
Environmental reserve, Ending Balance	$ 9.6