Separation Transaction and Discontinued Operations - Summary of Discontinued Operations in Statement of Consolidated Balance Sheet (Detail) $ in Millions	Dec. 31, 2015 USD ($)
Total assets of discontinued operations:
Current assets of discontinued operations	$ 2,556
Noncurrent assets of discontinued operations	14,598
Total liabilities of discontinued operations:
Current liabilities of discontinued operations	2,536
Noncurrent liabilities of discontinued operations	4,679
Alcoa Corporation [Member]
Total assets of discontinued operations:
Cash and cash equivalents	557
Receivables from customers	380
Other receivables	128
Inventories	1,158
Prepaid expenses and other current assets	333
Current assets of discontinued operations	2,556
Properties, plants, and equipment, net	9,390
Goodwill	152
Investments	1,472
Deferred income taxes	1,360
Other noncurrent assets	2,224
Noncurrent assets of discontinued operations	14,598
Total assets of discontinued operations	17,154
Total liabilities of discontinued operations:
Accounts payable, trade	1,379
Accrued compensation and retirement costs	440
Taxes, including income taxes	136
Other current liabilities	563
Long-term debt due within one year	18
Current liabilities of discontinued operations	2,536
Long-term debt less amount due within one year	207
Accrued pension benefits	1,373
Accrued other postretirement benefits	1,189
Other noncurrent liabilities and deferred credits	1,910
Noncurrent liabilities of discontinued operations	4,679
Total liabilities of discontinued operations	$ 7,215