Summary of Significant Accounting Policies Property, Plant and Equipment (Details)	12 Months Ended
	Dec. 31, 2018
Property, Plant and Equipment [Line Items]
Repair and maintenance expensing period	18 months
Finite-lived intangible asset, useful life	17 years
Minimum [Member]
Property, Plant and Equipment [Line Items]
Finite-lived intangible asset, useful life	15 years
Maximum [Member]
Property, Plant and Equipment [Line Items]
Finite-lived intangible asset, useful life	25 years
Buildings and Improvements [Member] \| Minimum [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life	5 years
Buildings and Improvements [Member] \| Maximum [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life	38 years
Production Equipment and Machinery [Member] \| Minimum [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life	2 years
Production Equipment and Machinery [Member] \| Maximum [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life	25 years
Office Furniture, Equipment and Other[Member] \| Minimum [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life	3 years
Office Furniture, Equipment and Other[Member] \| Maximum [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life	10 years

Aleris Corp 10-K