Restructuring and Other Charges - Narrative (Details) $ in Millions	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2018 USD ($) employee position	Sep. 30, 2017 USD ($) position	Sep. 30, 2018 USD ($) employee position	Sep. 30, 2017 USD ($) position	Dec. 31, 2017 USD ($) employee
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges	$ (2)	$ 19	$ 20	$ 118
Restructuring and other charges after tax and noncontrolling interest	$ 3	$ 13	$ 14	$ 99
Number of employees associated with layoff costs | position	85	124	125	800
Reversal of forfeited executive stock compensation				$ 13
Severance costs				$ 7
Cash payments made against the layoff reserves			$ 38		$ 65
Reversals of previously recorded layoff			10		$ 11
Minimum amount of cash payments expected to be paid beyond the end of the current annual period			18
Maximum amount of cash payments expected to be paid beyond the end of the current annual period			$ 20
Engineered Products and Solutions
Restructuring Cost and Reserve [Line Items]
Number of employees associated with layoff costs | position	65	111	89	350
Global Rolled Products
Restructuring Cost and Reserve [Line Items]
Number of employees associated with layoff costs | position		1		243
Transportation and Construction Solutions
Restructuring Cost and Reserve [Line Items]
Number of employees associated with layoff costs | position				133
Corporate
Restructuring Cost and Reserve [Line Items]
Number of employees associated with layoff costs | position	20	12	36	74
Acuna, Mexico
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges	$ 12		$ 12
Restructuring and other charges after tax	9		9
New York office
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges			5
Restructuring and other charges after tax			4
Fusina, Italy
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges				$ 60
Restructuring and other charges after tax				60
Postretirement Curtailment Benefit
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges	28		28
Restructuring and other charges after tax	22		22
Restructuring Programs Layoffs
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges	8	$ 11	16	59
Restructuring and other charges after tax	6	8	12	40
Pension Settlement
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges	4		4
Restructuring and other charges after tax	3		3
Other Miscellaneous Items
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges	3	8	7	7
Restructuring and other charges after tax	2	$ 5	5	5
Other Adjustments
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges	1		10	2
Restructuring and other charges after tax and noncontrolling interest	$ 1		8	2
Pension Curtailment Charge
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges			14
Restructuring and other charges after tax			$ 11
Reversal of Forfeited Executive Stock Compensation
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges				6
Restructuring and other charges after tax				$ 4
Restructuring Programs Layoffs 2018
Restructuring Cost and Reserve [Line Items]
Number of employees associated with layoff costs | employee			125
Approximate number of employees already laid off | employee	35		35
Cash payments made against the layoff reserves	$ 3		$ 6
Restructuring Programs Layoffs 2017
Restructuring Cost and Reserve [Line Items]
Number of employees associated with layoff costs | employee			760		830
Approximate number of employees already laid off | employee	570		570
Cash payments made against the layoff reserves	$ 4		$ 27
Restructuring Programs Layoffs 2016
Restructuring Cost and Reserve [Line Items]
Cash payments made against the layoff reserves	$ 0		$ 4