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Pension and Other Postretirement Benefits - Schedule of Obligations and Funded Status (Detail) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets at beginning of year $ 10,926    
Fair value of plan assets at end of year 4,646 $ 10,926  
Pension Benefits [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Benefit obligation at beginning of year 14,247    
Service cost 155 175 $ 166
Interest cost 431 577 630
Settlements 19 16 26
Curtailments   (9)  
Benefit obligation at end of year 7,026 14,247  
Funded status (2,360) (3,319)  
Less: Amounts attributed to joint venture partners   30  
Net funded status (2,360) (3,289)  
Noncurrent assets 6 9  
Noncurrent assets of discontinued operations   35  
Current liabilities (21) (23)  
Current liabilities of discontinued operations   (12)  
Noncurrent liabilities (2,345) (1,925)  
Noncurrent liabilities of discontinued operations   (1,373)  
Net amount recognized (2,360) (3,289)  
Net actuarial loss 2,979 5,351  
Prior service cost (benefit) 15 70  
Total, before tax effect 2,994 5,421  
Less: Amounts attributed to joint venture partners   38  
Net amount recognized, before tax effect 2,994 5,383  
Net actuarial loss (1,992) 440  
Amortization of accumulated net actuarial loss (380) (468)  
Prior service (benefit) cost (42) (7)  
Amortization of prior service (cost) benefit (13) (25)  
Total, before tax effect (2,427) (60)  
Less: Amounts attributed to joint venture partners (38) (5)  
Net amount recognized, before tax effect (2,389) (55)  
Pension Benefits [Member] | Change In Benefit Obligation [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Benefit obligation at beginning of year 14,247 15,019  
Service cost 165 187  
Interest cost 435 583  
Amendments 2 18  
Actuarial (gains) losses 770 (222)  
Acquisitions   188  
Transfer to Alcoa Corporation (7,577)    
Settlements (82) (72)  
Curtailments   (12)  
Benefits paid (794) (1,033)  
Foreign currency translation impact (140) (409)  
Benefit obligation at end of year 7,026 14,247 15,019
Pension Benefits [Member] | Change in Plan Assets [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets at beginning of year 10,928 11,717  
Actual return on plan assets 89 24  
Employer contributions 296 479  
Participants' contributions 16 21  
Settlements (82) (72)  
Benefits paid (762) (1,015)  
Administrative expenses (65) (55)  
Acquisitions   164  
Transfer to Alcoa Corporation (5,610)    
Foreign currency translation impact (144) (335)  
Fair value of plan assets at end of year 4,666 10,928 11,717
Other Postretirement Benefits [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Service cost 13 14 15
Interest cost 63 92 114
Curtailments   4  
Funded status (980) (2,319)  
Net funded status (980) (2,319)  
Current liabilities (91) (93)  
Current liabilities of discontinued operations   (120)  
Noncurrent liabilities (889) (917)  
Noncurrent liabilities of discontinued operations   (1,189)  
Net amount recognized (980) (2,319)  
Net actuarial loss 150 398  
Prior service cost (benefit) (45) (106)  
Total, before tax effect 105 292  
Net amount recognized, before tax effect 105 292  
Net actuarial loss (224) 23  
Amortization of accumulated net actuarial loss (24) (17)  
Prior service (benefit) cost 37 1  
Amortization of prior service (cost) benefit 24 37  
Total, before tax effect (187) 44  
Net amount recognized, before tax effect (187) 44  
Other Postretirement Benefits [Member] | Change In Benefit Obligation [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Benefit obligation at beginning of year 2,319 2,368  
Service cost 13 14  
Interest cost 63 92  
Actuarial (gains) losses 112 26  
Acquisitions   48  
Transfer to Alcoa Corporation (1,340)    
Curtailments   (6)  
Benefits paid (197) (235)  
Medicare Part D subsidy receipts 9 15  
Foreign currency translation impact 1 (3)  
Benefit obligation at end of year $ 980 $ 2,319 $ 2,368