Restructuring and Other Charges - 2018 Actions (Details) $ in Millions		3 Months Ended		12 Months Ended
	Oct. 31, 2018 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2019 USD ($) position	Dec. 31, 2018 USD ($) position	Dec. 31, 2017 USD ($) position
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges				$ 620	$ 9	$ 165
Restructuring and other charges after tax				512	9	143
Gain on disposition of assets, after tax					81
Gain (loss) on disposition of business, before tax				20	109	(57)
Gain (loss) on disposition of assets, before tax				(7)	(10)	$ 513
Number of employees associated with layoff costs | position						880
Cash payments for restructuring				79	49	$ 65
Engineered Products and Forgings
Restructuring Cost and Reserve [Line Items]
Number of employees associated with layoff costs | position						403
Pension Settlement Cost
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges				9	96
Restructuring and other charges after tax				7	75
Pension Curtailment Charge
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges					23
Restructuring and other charges after tax and noncontrolling interests					18
Postretirement Curtailment Benefit
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges					28
Restructuring and other charges after tax					22
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
Restructuring Programs Layoffs Two Thousand Eighteen
Restructuring Cost and Reserve [Line Items]
Number of employees associated with layoff costs | position					125
Cash payments for restructuring				$ 4	$ 9
Restructuring Programs Layoffs Two Thousand Eighteen | Engineered Products and Forgings
Restructuring Cost and Reserve [Line Items]
Number of employees associated with layoff costs | position					89
Facility Closing
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges					$ 12
Restructuring and other charges after tax					9
Other Adjustments
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges					8	$ (11)
Restructuring and other charges after tax and noncontrolling interests					4	(8)
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
Texarkana, Texas Rolling Mill And Cast House
Restructuring Cost and Reserve [Line Items]
Gain on disposition of assets, after tax					119
Gain (loss) on disposition of business, before tax	$ 154	$ 20
Texarkana, Texas Rolling Mill
Restructuring Cost and Reserve [Line Items]
Gain on disposition of assets, after tax		15	$ 119	17
Gain (loss) on disposition of business, before tax			154
Gain (loss) on disposition of assets, before tax		$ 20		20	154
Eger
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges after tax					39
Gain on disposition of assets, after tax			(39)
Gain (loss) on disposition of business, before tax			$ (43)	$ (43)	(43)
New York office | Facility Closing
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges					6
Restructuring and other charges after tax					$ 4
Corporate
Restructuring Cost and Reserve [Line Items]
Number of employees associated with layoff costs | position						141
Corporate | Restructuring Programs Layoffs Two Thousand Eighteen
Restructuring Cost and Reserve [Line Items]
Number of employees associated with layoff costs | position					36