Summary of Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2016

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
Bauxite		35		17
Alumina		30		27
Aluminum		36		22
Cast Products		33		19
Energy		34		25
Rolled Products		31		22

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
Bauxite		8		10
Alumina		7		19
Aluminum		6		38
Cast Products		3		—
Energy		4		37
Rolled Products		6		20