Summary of Significant Accounting Policies - Additional Information (Details)			1 Months Ended	3 Months Ended			12 Months Ended
	Dec. 31, 2017 USD ($) reporting_unit	Mar. 30, 2012 USD ($)	Jan. 31, 2018 reporting_unit	Dec. 31, 2018 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2018 USD ($) reporting_unit	Dec. 31, 2017 USD ($) reporting_unit	Dec. 31, 2016 USD ($) reporting_unit	Jan. 01, 2019 USD ($)
Summary Of Significant Accounting Policies [Line Items]
Original maturity of cash equivalents							3 months
Number of reporting units | reporting_unit	4		3				6		8
Segment allocation, goodwill recognized	$ 4,535,000,000			$ 4,500,000,000		$ 4,535,000,000	$ 4,500,000,000	$ 4,535,000,000	$ 5,148,000,000
Minimum percentage of estimated fair value of reporting unit to be less than carrying amount of goodwill							50.00%
Period required for impairment testing of reporting units							3 years
Impairment of goodwill (A and O)					$ 0		$ 0	719,000,000	0
Revenue, terms of payment, period							30 days
Businesses expected to be disposed within, years							1 year
Cash received for receivables		$ 50,000,000					$ 1,016,000,000	792,000,000	778,000,000
Payment for debt extinguishment or debt prepayment cost							17,000,000	52,000,000	3,000,000
Restricted cash	4,000,000			6,000,000		4,000,000	6,000,000	4,000,000	15,000,000
Net periodic benefit cost, non-service							$ 112,000,000	154,000,000	$ 135,000,000
Amount of stranded tax effects in accumulated other comprehensive income reclassified to accumulated deficit				367,000,000
Engineered Products and Solutions
Summary Of Significant Accounting Policies [Line Items]
Number of reporting units | reporting_unit									4
Number of reporting units for goodwill allocation | reporting_unit							3
Segment allocation, goodwill recognized	4,205,000,000			4,179,000,000		4,205,000,000	$ 4,179,000,000	4,205,000,000
Impairment of goodwill (A and O)						719,000,000		719,000,000
Engineered Products and Solutions | Alcoa Forging and Extrusions
Summary Of Significant Accounting Policies [Line Items]
Impairment of goodwill (A and O)				719,000,000
Transportation and Construction Solutions
Summary Of Significant Accounting Policies [Line Items]
Number of reporting units | reporting_unit									3
Segment allocation, goodwill recognized	78,000,000			76,000,000		78,000,000	76,000,000	78,000,000
Impairment of goodwill (A and O)								$ 0
Global Rolled Products
Summary Of Significant Accounting Policies [Line Items]
Number of reporting units | reporting_unit								1	1
Segment allocation, goodwill recognized	$ 252,000,000			245,000,000		$ 252,000,000	$ 245,000,000	$ 252,000,000
Impairment of goodwill (A and O)								$ 0
Minimum | Engineered Products and Solutions
Summary Of Significant Accounting Policies [Line Items]
Percentage of total goodwill allocated to two reporting units							90.00%
Arconic Engines
Summary Of Significant Accounting Policies [Line Items]
Segment allocation, goodwill recognized				2,065,000,000			$ 2,065,000,000
Arconic Fastening Systems
Summary Of Significant Accounting Policies [Line Items]
Segment allocation, goodwill recognized				1,607,000,000			1,607,000,000
Arconic Engineered Structures
Summary Of Significant Accounting Policies [Line Items]
Segment allocation, goodwill recognized				$ 507,000,000			$ 507,000,000
Disks Asset Group
Summary Of Significant Accounting Policies [Line Items]
Impairment of goodwill (A and O)					$ 0
Subsequent Event | Minimum
Summary Of Significant Accounting Policies [Line Items]
Right-of-use asset and operating lease liability										$ 300,000,000
Subsequent Event | Maximum
Summary Of Significant Accounting Policies [Line Items]
Right-of-use asset and operating lease liability										$ 340,000,000