Restructuring and Other Charges - Activity and Reserve Balances for Restructuring Charges (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Jun. 30, 2019	Dec. 31, 2018	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Restructuring Reserve [Roll Forward]
Restructuring reserve beginning balance			$ 13	$ 22	$ 33
Cash payments			(51)	(63)	(30)
Restructuring and other charges			182	582	163
Other			(90)	(528)	(144)
Restructuring reserve ending balance		$ 22	54	13	22
Restructuring and other charges			182	582	163
Net loss on divestitures of businesses			8	63	43
Gain (loss) on sale of assets			3	1
Benefit from termination of plan			3
Curtailment (charge) benefit					(9)
Impairment of assets to be disposed of			5
Accelerated depreciation			2
Pension benefits paid
Restructuring Reserve [Roll Forward]
Restructuring and other charges			69
Settlements			76	9	96
Curtailment (charge) benefit			0	0	(23)
Other postretirement benefits
Restructuring Reserve [Roll Forward]
Settlements			0	0	0
Curtailment (charge) benefit		(9)	2	58	28
Layoff costs
Restructuring Reserve [Roll Forward]
Restructuring reserve beginning balance			13	13	33
Cash payments			(51)	(63)	(30)
Restructuring and other charges			161	58	101
Other			(69)	5	(91)
Restructuring reserve ending balance		13	54	13	13
Restructuring and other charges			113	69
Layoff costs | Pension benefits paid
Restructuring Reserve [Roll Forward]
Settlements			74
Other exit costs
Restructuring Reserve [Roll Forward]
Restructuring reserve beginning balance			0	9	0
Cash payments			0	0	0
Restructuring and other charges			21	524	62
Other			(21)	(533)	(53)
Restructuring reserve ending balance		$ 9	0	0	9
Restructuring and other charges					3
Reclassification of pension costs
Restructuring Reserve [Roll Forward]
Restructuring and other charges					119
Credit in post-retirement costs
Restructuring Reserve [Roll Forward]
Restructuring and other charges					28
Facility Closing
Restructuring Reserve [Roll Forward]
Restructuring and other charges			6		9
Other Adjustments
Restructuring Reserve [Roll Forward]
Restructuring and other charges					4
Elimination Of Life Insurance Benefits
Restructuring Reserve [Roll Forward]
Restructuring and other charges				16
Other, Pension Settlement Cost
Restructuring Reserve [Roll Forward]
Restructuring and other charges				9
Impairment Of Disks
Restructuring Reserve [Roll Forward]
Restructuring and other charges	$ 428			428
Executive Severance Net Of The Benefit Of Forfeited Executive Stock Compensation
Restructuring Reserve [Roll Forward]
Restructuring and other charges				2
Asset Impairment Associated With The Sale Of Business
Restructuring Reserve [Roll Forward]
Restructuring and other charges				59
Impairment For Trade Name Intangible Asset And Fixed Assets
Restructuring Reserve [Roll Forward]
Restructuring and other charges				14
Other Exit Cost Lease Termination Loss
Restructuring Reserve [Roll Forward]
Restructuring and other charges				12
Other Miscellaneous Charges
Restructuring Reserve [Roll Forward]
Restructuring and other charges				7
Impairment Of A Cost Method Investment
Restructuring Reserve [Roll Forward]
Restructuring and other charges			5	5
Other Exit Costs, Reclassification Of Lease Exit Costs
Restructuring Reserve [Roll Forward]
Restructuring and other charges				$ 9
Asset Impairment Associated Facility Closure
Restructuring Reserve [Roll Forward]
Restructuring and other charges			1
Eger
Restructuring Reserve [Roll Forward]
Net loss on divestitures of businesses					$ 43
U.K. Forging Business | Facility Closing
Restructuring Reserve [Roll Forward]
Restructuring and other charges			$ 5