Restructuring and Other Charges - Narrative (Details) $ in Millions	3 Months Ended				9 Months Ended
	Sep. 30, 2020 USD ($) employee	Sep. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Sep. 30, 2020 USD ($) employee	Sep. 30, 2019 USD ($) employee
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges	$ 22	$ 56			$ 166	$ 572
Layoff costs	17	0			93	68
Accelerated depreciation	2	2			2
Settlements	3	4			67	(8)
Benefit from termination of deferred benefit plan	3				3
Gain (loss) on sale of assets		1			2	1
Impairment of assets to be disposed of					5
Non-cash asset impairments	0	8			0	442
Other exit costs						4
Disks Long-Lived Asset Group
Restructuring Cost and Reserve [Line Items]
Non-cash asset impairments			$ 428			428
Primary Research and Development Facility
Restructuring Cost and Reserve [Line Items]
Non-cash asset impairments						14
Small Additive Business
Restructuring Cost and Reserve [Line Items]
Gain (loss) on sale of assets						(12)
Other postretirement benefits
Restructuring Cost and Reserve [Line Items]
Curtailment benefit	2	0			2	58
Other postretirement benefits | US
Restructuring Cost and Reserve [Line Items]
Curtailment benefit				$ 58
Pension benefits
Restructuring Cost and Reserve [Line Items]
Settlements	8	4			72	8
Pension benefits | US
Restructuring Cost and Reserve [Line Items]
Settlements		4				8
Pension benefits | United Kingdom and United States
Restructuring Cost and Reserve [Line Items]
Settlements					72
Engine Products | Disks Long-Lived Asset Group
Restructuring Cost and Reserve [Line Items]
Non-cash asset impairments			247			247
Engineered Structures | Disks Long-Lived Asset Group
Restructuring Cost and Reserve [Line Items]
Non-cash asset impairments			$ 181			181
Layoff costs
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges	$ 17				$ 150	$ 68
Number of employees associated with layoff costs | employee	791				3,772	901
Layoff costs | Corporate expense
Restructuring Cost and Reserve [Line Items]
Number of employees associated with layoff costs | employee					23	494
Layoff costs | Engine Products
Restructuring Cost and Reserve [Line Items]
Number of employees associated with layoff costs | employee	415				1,706	103
Layoff costs | Engineered Structures
Restructuring Cost and Reserve [Line Items]
Number of employees associated with layoff costs | employee	376				676	112
Layoff costs | Fastening Systems
Restructuring Cost and Reserve [Line Items]
Number of employees associated with layoff costs | employee					1,275	132
Layoff costs | Forged Wheels
Restructuring Cost and Reserve [Line Items]
Number of employees associated with layoff costs | employee					92	60
Facility closing
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges					$ 5
Facility closing | U.K. Forging Business
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges		$ 43			6	$ 43
Lease terminations
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges						12
Executive severance
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges						2
Employee severance, life insurance benefits
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges						(16)
Reversal of prior period programs
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges					$ (10)	$ (2)