Restructuring and Other Charges - 2019 Actions (Details) $ in Millions	3 Months Ended			12 Months Ended
	Dec. 31, 2019 USD ($) position	Jun. 30, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2019 USD ($) position	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($) position
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges				$ 620	$ 9	$ 165
Restructuring and other charges after tax				512	9	143
Non-cash asset impairments				570	13	$ 58
Asset impairment charges, net of tax				477
Number of employees associated with layoff costs | position						880
Gain (loss) on disposition of assets, before tax				(7)	(10)	$ 513
Gain on disposition of assets, after tax					81
Cash payments for restructuring				79	49	65
Impairment Of Disks
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges		$ 428		428
Restructuring and other charges after tax				345
Asset Impairment Associated With The Sale Of Business
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges				112
Restructuring and other charges after tax				109
Sale Of Company's Brazilian Rolling Mill Operations
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges				53
UK Forgings
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges				46
Small Additive Business
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges				13
Impairment For Trade Name Intangible Asset And Fixed Assets
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges				25
Restructuring and other charges after tax				19
Impairment Of A Cost Method Investment
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges				5
Restructuring and other charges after tax				4
Restructuring Programs Layoffs
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges				103	20
Restructuring and other charges after tax				$ 78	17
Number of employees associated with layoff costs | position				1,310
Other Exit Costs
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges				$ 26	19	69
Restructuring and other charges after tax				21	15	47
Cash payments for restructuring				5	2	6
Corporate Aircraft
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges				12
Restructuring, Accelerated Depreciation
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges				9
Executive Severance Net Of The Benefit Of Forfeited Executive Stock Compensation
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges				2
Various Other Exit Costs
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges				4
Pension Settlement Cost
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges				9	96
Restructuring and other charges after tax				7	75
Elimination Of Life Insurance Benefits
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges				(58)
Restructuring and other charges after tax				(45)
Employee Severance
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges				(10)
Restructuring and other charges after tax				(9)
Cash payments for restructuring				$ 74	47	$ 59
Restructuring Programs Layoffs 2019
Restructuring Cost and Reserve [Line Items]
Number of employees associated with layoff costs | position				1,310
Approximate number of employees already laid off | position	947			947
Cash payments for restructuring				$ 65
Global Rolled Products
Restructuring Cost and Reserve [Line Items]
Number of employees associated with layoff costs | position						336
Global Rolled Products | Restructuring Programs Layoffs
Restructuring Cost and Reserve [Line Items]
Number of employees associated with layoff costs | position				484
Corporate Segment | Restructuring Programs Layoffs
Restructuring Cost and Reserve [Line Items]
Number of employees associated with layoff costs | position				460
Engineered Products And Solutions | Restructuring Programs Layoffs
Restructuring Cost and Reserve [Line Items]
Number of employees associated with layoff costs | position				366
Texarkana, Texas Rolling Mill
Restructuring Cost and Reserve [Line Items]
Gain (loss) on disposition of assets, before tax	$ 20			$ 20	$ 154
Gain on disposition of assets, after tax	$ 15		$ 119	$ 17