Restructuring and Other Charges - Narrative (Details) $ in Millions	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2019 USD ($) position	Jun. 30, 2018 USD ($) position	Jun. 30, 2019 USD ($) position	Jun. 30, 2018 USD ($) position	Dec. 31, 2020 USD ($)	Dec. 31, 2018 USD ($) position
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges (benefits)	$ 499	$ 15	$ 511	$ 22
Restructuring and other charges (benefits) after tax	397	12	407	17
Cash payments for restructuring			43			$ 49
Impairment Of Disks
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges (benefits)	428		428
Restructuring and other charges (benefits) after tax	345		345
Restructuring Programs Layoffs
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges (benefits)	30	4	95	8
Restructuring and other charges (benefits) after tax	$ 22	3	$ 73	$ 6
Number of employees associated with layoff costs | position	350		1,127	40
Impairment for a trade name intangible asset and fixed assets
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges (benefits)	$ 16		$ 16
Restructuring and other charges (benefits) after tax	12		12
Other exit costs
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges (benefits)	12		12	$ 4
Restructuring and other charges (benefits) after tax	9		9	3
Cash payments for restructuring			3			2
Loss On Sale Related To Small Additive Business
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges (benefits)	12		12
Restructuring and other charges (benefits) after tax	9		9
Restructuring, Accelerated Depreciation
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges (benefits)	2		2
Restructuring and other charges (benefits) after tax	2		2
Pension Settlement Cost
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges (benefits)	2		4
Restructuring and other charges (benefits) after tax	1		3
Layoff costs
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges (benefits)	(3)	(5)	(3)
Restructuring and other charges (benefits) after tax	$ (3)	(4)	(3)
Cash payments for restructuring			40			$ 47
Executive Severance Net Of The Benefit Of Forfeited Executive Stock Compensation
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges (benefits)			2
Restructuring and other charges (benefits) after tax			1
Other Miscellaneous Charges
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges (benefits)		2	1
Restructuring and other charges (benefits) after tax		2	1
Elimination Of Life Insurance Benefits
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges (benefits)			(58)
Restructuring and other charges (benefits) after tax			$ (45)
Pension Curtailment Charge
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges (benefits)		9		14
Restructuring and other charges (benefits) after tax		7		11
New York
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges (benefits)		5		5
Restructuring and other charges (benefits) after tax		$ 4		4
Other Adjustments
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges (benefits)				9
Restructuring and other charges (benefits) after tax				$ 7
Restructuring Programs Layoffs 2019
Restructuring Cost and Reserve [Line Items]
Number of employees associated with layoff costs | position			1,127			1,150
Approximate number of employees already laid off | position	583		583
Cash payments for restructuring	$ 26		$ 40
Transportation and Construction Solutions | Restructuring Programs Layoffs
Restructuring Cost and Reserve [Line Items]
Number of employees associated with layoff costs | position	131		252
Engineered Products and Solutions | Restructuring Programs Layoffs
Restructuring Cost and Reserve [Line Items]
Number of employees associated with layoff costs | position	125	24	301	24
Corporate Segment | Restructuring Programs Layoffs
Restructuring Cost and Reserve [Line Items]
Number of employees associated with layoff costs | position	69		463	16
Global Rolled Products | Restructuring Programs Layoffs
Restructuring Cost and Reserve [Line Items]
Number of employees associated with layoff costs | position	25		111
Scenario, Forecast | Layoff costs
Restructuring Cost and Reserve [Line Items]
Cash payments for restructuring					$ 15