Properties, Plants, and Equipment, Net (Details) - USD ($)	3 Months Ended	12 Months Ended
	Jun. 30, 2018	Dec. 31, 2018	Dec. 31, 2017
Property, Plant and Equipment [Line Items]
Properties, plants, and equipment, gross		$ 11,734,000,000	$ 11,365,000,000
Less: accumulated depreciation and amortization		6,769,000,000	6,392,000,000
Properties plants and equipment excluding construction work in progress		4,965,000,000	4,973,000,000
Construction work-in-progress		739,000,000	621,000,000
Properties, plants, and equipment, net		5,704,000,000	5,594,000,000
Land and land rights
Property, Plant and Equipment [Line Items]
Properties, plants, and equipment, gross		136,000,000	140,000,000
Structures
Property, Plant and Equipment [Line Items]
Properties, plants, and equipment, gross		2,364,000,000	2,395,000,000
Machinery and equipment:
Property, Plant and Equipment [Line Items]
Properties, plants, and equipment, gross		9,234,000,000	8,830,000,000
Arconic Engines
Property, Plant and Equipment [Line Items]
Assets	$ 515,000,000
Percentage of fair value in excess of carrying amount	13.00%
Asset impairment charges	$ 0
Effect of one percentage point decrease on undiscounted cash flows		6,000,000
Total segment sales | Structures | Engineered Products and Solutions
Property, Plant and Equipment [Line Items]
Properties, plants, and equipment, gross		796,000,000	784,000,000
Total segment sales | Structures | Global Rolled Products
Property, Plant and Equipment [Line Items]
Properties, plants, and equipment, gross		1,068,000,000	1,090,000,000
Total segment sales | Structures | Transportation and Construction Solutions
Property, Plant and Equipment [Line Items]
Properties, plants, and equipment, gross		248,000,000	268,000,000
Total segment sales | Machinery and equipment: | Engineered Products and Solutions
Property, Plant and Equipment [Line Items]
Properties, plants, and equipment, gross		3,437,000,000	3,054,000,000
Total segment sales | Machinery and equipment: | Global Rolled Products
Property, Plant and Equipment [Line Items]
Properties, plants, and equipment, gross		4,629,000,000	4,641,000,000
Total segment sales | Machinery and equipment: | Transportation and Construction Solutions
Property, Plant and Equipment [Line Items]
Properties, plants, and equipment, gross		748,000,000	777,000,000
Other
Property, Plant and Equipment [Line Items]
Properties, plants, and equipment, net		305,000,000	310,000,000
Other | Structures
Property, Plant and Equipment [Line Items]
Properties, plants, and equipment, gross		252,000,000	253,000,000
Other | Machinery and equipment:
Property, Plant and Equipment [Line Items]
Properties, plants, and equipment, gross		$ 420,000,000	$ 358,000,000