Commitments and Contingencies - Environmental Matters (Details)		12 Months Ended
	May 09, 2017	Dec. 31, 2002 USD ($) a Participant	Dec. 31, 2020 USD ($) environmental_matter	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Oct. 31, 2001 USD ($)
Site Contingency [Line Items]
Number of environmental remediation matters (over) | environmental_matter			40
Accrued environmental costs			$ 300,600,000	$ 309,200,000	$ 327,900,000	$ 341,400,000
Guarantee obligations			120,000,000.0
Sacramento, California | Previously Reported | Environmental Protection Agency
Site Contingency [Line Items]
Non-contaminated land | a		2,600
Various Environmental Matters
Site Contingency [Line Items]
Accrued environmental costs			300,600,000
Various Environmental Matters | Sacramento, California
Site Contingency [Line Items]
Accrued environmental costs			208,400,000
Various Environmental Matters | Sacramento, California | Previously Reported
Site Contingency [Line Items]
Guarantee obligations		$ 20,000,000
Various Environmental Matters | Baldwin Park Operable Unit
Site Contingency [Line Items]
Accrued environmental costs			$ 76,200,000
Guarantee obligations							$ 25,000,000
Various Environmental Matters | Baldwin Park Operable Unit | Aerojet Rocketdyne Inc
Site Contingency [Line Items]
Number of other potentially responsible parties | Participant		7
Number of counterparties | Participant		5
Project agreement term (years)	10 years
Percentage of responsibility in all project costs			74.00%
Various Environmental Matters | Contracting business
Site Contingency [Line Items]
Environmental obligation funding percent			99.00%
Various Environmental Matters | Minimum
Site Contingency [Line Items]
Estimated environmental costs			$ 300,600,000
Various Environmental Matters | Minimum | Sacramento, California
Site Contingency [Line Items]
Estimated environmental costs			208,400,000
Various Environmental Matters | Minimum | Baldwin Park Operable Unit
Site Contingency [Line Items]
Estimated environmental costs			76,200,000
Various Environmental Matters | Maximum
Site Contingency [Line Items]
Estimated environmental costs			451,100,000
Various Environmental Matters | Maximum | Sacramento, California
Site Contingency [Line Items]
Estimated environmental costs			331,400,000
Guarantee obligations		$ 75,000,000
Various Environmental Matters | Maximum | Baldwin Park Operable Unit
Site Contingency [Line Items]
Estimated environmental costs			$ 91,900,000