Segment Information - Schedule of Operating Results of Alcoa's Reportable Segment (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Segment Reporting Information [Line Items]
Total sales	$ 5,836	$ 5,849	$ 11,290	$ 11,682
Equity loss	(30)	(10)	(68)	(22)
Depreciation, depletion, and amortization	328	341	647	682
Income taxes	167	115	321	253
After-tax operating income (ATOI)	418	304	743	655
Operating Segments [Member]
Segment Reporting Information [Line Items]
Total sales	7,024	7,088	13,700	14,247
Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Intersegment sales	1,242	1,301	2,529	2,674
Third-Party Sales [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Third-party sales	5,782	5,787	11,171	11,573
Alumina [Member]
Segment Reporting Information [Line Items]
Equity loss	(7)	(1)	(12)
Depreciation, depletion, and amortization	100	115	197	224
Income taxes	12	14	52	28
After-tax operating income (ATOI)	38	64	130	122
Alumina [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total sales	1,241	1,403	2,596	2,824
Alumina [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Intersegment sales	480	581	990	1,176
Alumina [Member] | Third-Party Sales [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Third-party sales	761	822	1,606	1,648
Primary Metals [Member]
Segment Reporting Information [Line Items]
Equity loss	(17)	(7)	(45)	(16)
Depreciation, depletion, and amortization	129	132	253	267
Income taxes	30	(25)	19	(24)
After-tax operating income (ATOI)	97	(32)	82	7
Primary Metals [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total sales	2,377	2,297	4,535	4,782
Primary Metals [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Intersegment sales	718	677	1,452	1,404
Primary Metals [Member] | Third-Party Sales [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Third-party sales	1,659	1,620	3,083	3,378
Global Rolled Products [Member]
Segment Reporting Information [Line Items]
Equity loss	(6)	(2)	(11)	(6)
Depreciation, depletion, and amortization	58	55	116	112
Income taxes	23	32	57	71
After-tax operating income (ATOI)	79	79	138	160
Global Rolled Products [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total sales	1,904	1,920	3,624	3,750
Global Rolled Products [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Intersegment sales	44	43	87	94
Global Rolled Products [Member] | Third-Party Sales [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Third-party sales	1,860	1,877	3,537	3,656
Engineered Products and Solutions [Member]
Segment Reporting Information [Line Items]
Depreciation, depletion, and amortization	41	39	81	79
Income taxes	102	94	193	178
After-tax operating income (ATOI)	204	193	393	366
Engineered Products and Solutions [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total sales	1,502	1,468	2,945	2,891
Engineered Products and Solutions [Member] | Third-Party Sales [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Third-party sales	$ 1,502	$ 1,468	$ 2,945	$ 2,891