Commitments and Contingencies - Summary of Environmental Reserve Activity (Details) $ in Millions	3 Months Ended
	Mar. 31, 2022 USD ($)
Accrual for Environmental Loss Contingencies [Roll Forward]
Beginning balance	$ 296.4
Additions/Adjustments	3.6
Expenditures	(6.3)
Ending balance	293.7
Aerojet Rocketdyne- Sacramento
Accrual for Environmental Loss Contingencies [Roll Forward]
Beginning balance	214.7
Additions/Adjustments	3.8
Expenditures	(3.3)
Ending balance	215.2
Aerojet Rocketdyne- BPOU
Accrual for Environmental Loss Contingencies [Roll Forward]
Beginning balance	64.7
Additions/Adjustments	(0.4)
Expenditures	(2.7)
Ending balance	61.6
Other Aerojet Rocketdyne Sites
Accrual for Environmental Loss Contingencies [Roll Forward]
Beginning balance	11.8
Additions/Adjustments	0.2
Expenditures	(0.3)
Ending balance	11.7
Total Aerojet Rocketdyne
Accrual for Environmental Loss Contingencies [Roll Forward]
Beginning balance	291.2
Additions/Adjustments	3.6
Expenditures	(6.3)
Ending balance	288.5
Other
Accrual for Environmental Loss Contingencies [Roll Forward]
Beginning balance	5.2
Additions/Adjustments	0.0
Expenditures	0.0
Ending balance	$ 5.2