Segment Information - Assets By Reportable Segment (Details) - USD ($) $ in Millions	Jun. 30, 2019	Dec. 31, 2018
Segment Reporting Information [Line Items]
Total assets	$ 17,913	$ 18,693
Operating Segments
Segment Reporting Information [Line Items]
Total assets	15,611	15,372
Engineered Products and Solutions
Segment Reporting Information [Line Items]
Total assets	9,681	9,797
Global Rolled Products
Segment Reporting Information [Line Items]
Total assets	4,714	4,486
Transportation and Construction Solutions
Segment Reporting Information [Line Items]
Total assets	$ 1,216	$ 1,089