Commitments and Contingencies - Summary of Environmental Reserve Activity (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Accrual for Environmental Loss Contingencies [Roll Forward]
Beginning balance	$ 300.6	$ 309.2	$ 327.9
Additions	35.3	32.4	16.7
Expenditures	(39.5)	(41.0)	(35.4)
Ending balance	296.4	300.6	309.2
Aerojet Rocketdyne- Sacramento
Accrual for Environmental Loss Contingencies [Roll Forward]
Beginning balance	208.4	203.6	207.4
Additions	28.8	30.9	17.0
Expenditures	(22.5)	(26.1)	(20.8)
Ending balance	214.7	208.4	203.6
Aerojet Rocketdyne- BPOU
Accrual for Environmental Loss Contingencies [Roll Forward]
Beginning balance	76.2	89.6	103.8
Additions	2.5	(0.2)	(0.8)
Expenditures	(14.0)	(13.2)	(13.4)
Ending balance	64.7	76.2	89.6
Other Aerojet Rocketdyne Sites
Accrual for Environmental Loss Contingencies [Roll Forward]
Beginning balance	10.6	11.8	12.4
Additions	3.7	0.0	0.3
Expenditures	(2.5)	(1.2)	(0.9)
Ending balance	11.8	10.6	11.8
Total Aerojet Rocketdyne
Accrual for Environmental Loss Contingencies [Roll Forward]
Beginning balance	295.2	305.0	323.6
Additions	35.0	30.7	16.5
Expenditures	(39.0)	(40.5)	(35.1)
Ending balance	291.2	295.2	305.0
Other
Accrual for Environmental Loss Contingencies [Roll Forward]
Beginning balance	5.4	4.2	4.3
Additions	0.3	1.7	0.2
Expenditures	(0.5)	(0.5)	(0.3)
Ending balance	$ 5.2	$ 5.4	$ 4.2