Summary of Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2015

Accounting Policies [Abstract]

Weighted-Average Useful Lives of Structures and Machinery and Equipment

The following table details the weighted-average useful lives of structures and machinery and equipment by reporting segment (numbers in years):

Segment	Structures		Machinery and equipment
Alumina:
Alumina refining		30		27
Bauxite mining		34		17
Primary Metals:
Aluminum smelting		36		22
Power generation		31		22
Global Rolled Products		31		21
Engineered Products and Solutions		29		18
Transportation and Construction Solutions		28		19

Weighted-Average Useful Lives of Software and Other Intangible Assets

The following table details the weighted-average useful lives of software and other intangible assets by reporting segment (numbers in years):

Segment	Software		Other intangible assets
Alumina		7		15
Primary Metals		6		37
Global Rolled Products		9		14
Engineered Products and Solutions		7		32
Transportation and Construction Solutions		8		23