Cash Flow Information - Additional Information (Detail) $ / shares in Units, $ in Millions						1 Months Ended					3 Months Ended	12 Months Ended			14 Months Ended
	Oct. 02, 2017 $ / shares shares	Oct. 05, 2016 $ / shares shares	Aug. 31, 2016 shares	Jul. 23, 2015 shares	Jul. 22, 2015 shares	Aug. 31, 2016 shares	Aug. 31, 2016 USD ($) shares	Aug. 30, 2016 USD ($)	Jul. 31, 2015 USD ($) shares	Sep. 30, 2014 shares	Jun. 30, 2017 USD ($) shares	Dec. 31, 2017 USD ($) shares	Dec. 31, 2016 USD ($) shares	Dec. 31, 2015 USD ($) shares	Oct. 04, 2016 shares	Dec. 31, 2014 shares
Schedule Of Common Stock [Line Items]
Sales of investments												$ 890	$ 280	$ 40
Proceeds from sale of company-owned life insurance policies													457
Proceeds from Divestiture of Businesses												$ (9)	$ 692	$ 112
Depository shares sold (in shares) | shares	24,022									25,000,000	12,958,767
Interest in preferred stock	0.10									0.10
Conversion of stock, shares converted (in shares) | shares	31,420
Reverse stock split ratio		0.3333
Common stock share outstanding (in shares) | shares		400,000,000										481,416,537	438,519,780	1,310,160,141	1,300,000,000.0	1,216,663,661
Common stock par value (usd per share) | $ / shares		$ 1
Decrease in common stock due to reverse stock split													$ (877)
Treasury stock retirement (in shares) | shares			25,000,000			76,000,000	76,000,000
Retirement of treasury stock								$ 76					0
Increase in additional paid in capital due to reverse stock split													877
Common stock conversion transaction value												$ 0	0	$ 870
Common stock
Schedule Of Common Stock [Line Items]
Retirement of treasury stock							$ 76	76					76
Number of common stock shares issued in a part of acquisition (in shares) | shares														87,397,414
Additional capital
Schedule Of Common Stock [Line Items]
Retirement of treasury stock							$ 2,563	$ 2,563					2,563
RTI
Schedule Of Common Stock [Line Items]
Common stock conversion transaction value									$ 870
Number of common stock shares issued in a part of acquisition (in shares) | shares		29,000,000		87,397,414	29,132,471				29,132,471						87,000,000
Remmele Medical
Schedule Of Common Stock [Line Items]
Proceeds from Divestiture of Businesses													(102)
Alcoa Corporation
Schedule Of Common Stock [Line Items]
Sales of investments													145
Proceeds from Divestiture of Businesses													120
Alcoa Corporation | Electricity Contract
Schedule Of Common Stock [Line Items]
Outstanding notes held by Investment banks, including accrued and unpaid interest											$ 465
Mandatory convertible preferred stock
Schedule Of Common Stock [Line Items]
Depository shares sold (in shares) | shares	24,975,978
Interest in preferred stock	0.1
Preferred stock conversion price (in usd per share) | $ / shares	$ 1.56996
Conversion of stock, shares converted (in shares) | shares	39,211,286
Exchange Traded Fixed Income and Equity Securities
Schedule Of Common Stock [Line Items]
Sales of investments													$ 130