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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 |  |

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