Goodwill and Other Intangible Assets - Changes in Carrying Amount of Goodwill (Details) - USD ($)	3 Months Ended			12 Months Ended
	Dec. 31, 2018	Mar. 31, 2018	Dec. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Goodwill [Roll Forward]
Goodwill gross, beginning balance		$ 5,307,000,000		$ 5,307,000,000	$ 5,201,000,000
Accumulated impairment losses		(772,000,000)		(772,000,000)	(53,000,000)
Goodwill, net		4,535,000,000		4,535,000,000	5,148,000,000
Acquisitions and Divestitures				(1,000,000)
Impairment		0		0	(719,000,000)	$ 0
Translation and other				(34,000,000)	106,000,000
Goodwill gross, ending balance	$ 5,272,000,000		$ 5,307,000,000	5,272,000,000	5,307,000,000	5,201,000,000
Accumulated impairment losses	(772,000,000)		(772,000,000)	(772,000,000)	(772,000,000)	(53,000,000)
Goodwill, ending balance	4,500,000,000	4,535,000,000	4,535,000,000	4,535,000,000	5,148,000,000	5,148,000,000
Engineered Products and Solutions
Goodwill [Roll Forward]
Goodwill, net		4,205,000,000		4,205,000,000
Acquisitions and Divestitures				(1,000,000)
Impairment			(719,000,000)		(719,000,000)
Goodwill, ending balance	4,179,000,000	4,205,000,000	4,205,000,000	4,205,000,000
Global Rolled Products
Goodwill [Roll Forward]
Goodwill, net		252,000,000		252,000,000
Acquisitions and Divestitures				0
Impairment					0
Goodwill, ending balance	245,000,000	252,000,000	252,000,000	252,000,000
Transportation and Construction Solutions
Goodwill [Roll Forward]
Goodwill, net		78,000,000		78,000,000
Acquisitions and Divestitures				0
Impairment					0
Goodwill, ending balance	76,000,000	78,000,000	78,000,000	78,000,000
Total segment sales | Engineered Products and Solutions
Goodwill [Roll Forward]
Goodwill gross, beginning balance		4,924,000,000		4,924,000,000	4,832,000,000
Accumulated impairment losses		(719,000,000)		(719,000,000)	0
Goodwill, net		4,205,000,000		4,205,000,000	4,832,000,000
Translation and other				(25,000,000)	92,000,000
Goodwill gross, ending balance	4,898,000,000		4,924,000,000	4,898,000,000	4,924,000,000	4,832,000,000
Accumulated impairment losses	(719,000,000)		(719,000,000)	(719,000,000)	(719,000,000)	0
Goodwill, ending balance	4,179,000,000	4,205,000,000	4,205,000,000	4,205,000,000	4,832,000,000	4,832,000,000
Total segment sales | Global Rolled Products
Goodwill [Roll Forward]
Goodwill gross, beginning balance		252,000,000		252,000,000	241,000,000
Accumulated impairment losses		0		0	0
Goodwill, net		252,000,000		252,000,000	241,000,000
Translation and other				(7,000,000)	11,000,000
Goodwill gross, ending balance	245,000,000		252,000,000	245,000,000	252,000,000	241,000,000
Accumulated impairment losses	0		0	0	0	0
Goodwill, ending balance	245,000,000	252,000,000	252,000,000	252,000,000	241,000,000	241,000,000
Total segment sales | Transportation and Construction Solutions
Goodwill [Roll Forward]
Goodwill gross, beginning balance		131,000,000		131,000,000	128,000,000
Accumulated impairment losses		(53,000,000)		(53,000,000)	(53,000,000)
Goodwill, net		78,000,000		78,000,000	75,000,000
Translation and other				(2,000,000)	3,000,000
Goodwill gross, ending balance	129,000,000		131,000,000	129,000,000	131,000,000	128,000,000
Accumulated impairment losses	(53,000,000)		(53,000,000)	(53,000,000)	(53,000,000)	(53,000,000)
Goodwill, ending balance	$ 76,000,000	$ 78,000,000	$ 78,000,000	$ 78,000,000	$ 75,000,000	$ 75,000,000