Segment Information - Assets By Reportable Segment (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Segment Reporting Information [Line Items]
Total assets	$ 18,361	$ 18,693
Operating Segments
Segment Reporting Information [Line Items]
Total assets	16,127	15,372
Engineered Products and Solutions
Segment Reporting Information [Line Items]
Total assets	10,153	9,797
Global Rolled Products
Segment Reporting Information [Line Items]
Total assets	4,768	4,486
Transportation and Construction Solutions
Segment Reporting Information [Line Items]
Total assets	$ 1,206	$ 1,089