Commitments and Contingencies - Summary of Environmental Reserve Activity (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Nov. 30, 2013	Nov. 30, 2012	Nov. 30, 2011
Commitment And Contingencies [Line Items]
Environmental reserve, Beginning Balance	$ 189.5	$ 190.6	$ 217.7
Additions	18.8	34.7	32.9
Expenditures	(37.0)	(35.8)	(60.0)
Environmental reserve, Ending Balance	171.3	189.5	190.6
Aerojet - Sacramento [Member]
Commitment And Contingencies [Line Items]
Environmental reserve, Beginning Balance	140.5	130.7	139.8
Additions	9.8	24.5	21.2
Expenditures	(22.3)	(14.7)	(30.3)
Environmental reserve, Ending Balance	128.0	140.5	130.7
Aerojet - BPOU [Member]
Commitment And Contingencies [Line Items]
Environmental reserve, Beginning Balance	31.2	38.6	46.1
Additions	5.1	5.9	5.9
Expenditures	(9.4)	(13.3)	(13.4)
Environmental reserve, Ending Balance	26.9	31.2	38.6
Other Aerojet Sites [Member]
Commitment And Contingencies [Line Items]
Environmental reserve, Beginning Balance	10.8	12.1	20.1
Additions	0.1	3.8	5.9
Expenditures	(2.7)	(5.1)	(13.9)
Environmental reserve, Ending Balance	8.2	10.8	12.1
Total Aerojet [Member]
Commitment And Contingencies [Line Items]
Environmental reserve, Beginning Balance	182.5	181.4	206.0
Additions	15.0	34.2	33.0
Expenditures	(34.4)	(33.1)	(57.6)
Environmental reserve, Ending Balance	163.1	182.5	181.4
Other [Member]
Commitment And Contingencies [Line Items]
Environmental reserve, Beginning Balance	7.0	9.2	11.7
Additions	3.8	0.5	(0.1)
Expenditures	(2.6)	(2.7)	(2.4)
Environmental reserve, Ending Balance	$ 8.2	$ 7.0	$ 9.2