Basis of Presentation (Tables)

9 Months Ended

12 Months Ended

Sep. 30, 2016

Dec. 31, 2015

Accounting Policies [Abstract]

Schedule of Cost Allocation

The following table reflects the allocations of those detailed above:

	Third quarter ended September 30,				Nine months ended September 30,
	2016		2015		2016			2015
Cost of goods sold*	$	13	$	22	$	39		$	70
Selling, general administrative, and other expenses		47		43		124			112
Research and development expenses		—		4		2			14
Provision for depreciation, depletion, and amortization		5		6		15			18
Restructuring and other charges**		1		5		1			15
Interest expense		59		63		178			190
Other (income) expenses, net		1		7		(8	)		9

* Allocation principally relates to ParentCo’s retained pension and other postemployment benefits expenses for closed and sold operations.

** Allocation primarily relates to layoff programs for ParentCo employees.

The following table reflects the allocations of those detailed above:

	Amount allocated to Alcoa Corporation
	2015		2014		2013
Cost of goods sold(1)	$	93	$	76	$	109
Selling, general administrative, and other expenses		146		158		154
Research and development expenses		17		21		16
Provision for depreciation, depletion, and amortization		22		37		38
Restructuring and other charges(2)		32		23		14
Interest expense		245		278		272
Other expenses (income), net		12		5		(1	)

(1) Allocation relates to ParentCo’s retained pension and Other postemployment benefits expenses for closed and sold operations.

(2) Allocation primarily relates to layoff programs for ParentCo employees.

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		34		17
Alumina		30		27
Aluminum		36		22
Cast Products		36		22
Energy		31		22
Rolled Products		31		21

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	7	15
Alumina	7	15
Aluminum	6	37
Cast Products	6	37
Energy	6	37
Rolled Products	9	14