Restructuring and Other Charges - Narrative (Details) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2019 USD ($) position	Mar. 31, 2018 USD ($) position	Dec. 31, 2020 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 position
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges (benefits)	$ 12	$ 7
Restructuring and other charges (benefits) after tax	10	5
Cash payments for restructuring	17			$ 49
Restructuring Programs Layoffs
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges (benefits)	65	4
Restructuring and other charges (benefits) after tax	$ 51	3
Number of employees associated with layoff costs | position	800
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
Pension Settlement Cost
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges (benefits)	2
Restructuring and other charges (benefits) after tax	2
Other Miscellaneous Charges
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges (benefits)	1
Restructuring and other charges (benefits) after tax	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)		5
Restructuring and other charges after tax and noncontrolling interest		4
Other Adjustments
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges (benefits)		2
Restructuring and other charges after tax and noncontrolling interest		1
Other exit costs
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges (benefits)		(4)
Restructuring and other charges (benefits) after tax		$ (3)
Cash payments for restructuring	$ 3			2
Restructuring Programs Layoffs 2019
Restructuring Cost and Reserve [Line Items]
Approximate number of employees already laid off | position	247
Number of employees associated with layoff costs | position					800
Cash payments for restructuring	$ 7
Restructuring Programs Layoffs 2018
Restructuring Cost and Reserve [Line Items]
Approximate number of employees already laid off | position	115
Number of employees associated with layoff costs | position					125
Cash payments for restructuring	$ 3
Restructuring Programs Layoffs 2017
Restructuring Cost and Reserve [Line Items]
Approximate number of employees already laid off | position	570
Number of employees associated with layoff costs | position					660
Cash payments for restructuring	$ 4
Layoff costs
Restructuring Cost and Reserve [Line Items]
Cash payments for restructuring	$ 14			$ 47
Corporate Segment | Restructuring Programs Layoffs
Restructuring Cost and Reserve [Line Items]
Number of employees associated with layoff costs | position	425
Corporate Segment | Restructuring Programs Layoffs 2018
Restructuring Cost and Reserve [Line Items]
Number of employees associated with layoff costs | position		16
Engineered Products and Solutions | Restructuring Programs Layoffs
Restructuring Cost and Reserve [Line Items]
Number of employees associated with layoff costs | position	168
Transportation and Construction Solutions | Restructuring Programs Layoffs
Restructuring Cost and Reserve [Line Items]
Number of employees associated with layoff costs | position	121
Global Rolled Products | Restructuring Programs Layoffs
Restructuring Cost and Reserve [Line Items]
Number of employees associated with layoff costs | position	86
Scenario, Forecast | Layoff costs
Restructuring Cost and Reserve [Line Items]
Cash payments for restructuring			$ 3