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Separation Transaction and Discontinued Operations - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Millions			3 Months Ended
	Feb. 14, 2017	Nov. 01, 2016	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Common stock sold	23,353,000
Common stock sold per share	$ 38.03
Cash proceeds sale of common stock	$ 888
Pre-tax gain on sale of common stock	$ 351
Investment in common stock of Alcoa Corporation				$ 446	$ 1,020
Yadkin [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds from sale of assets				$ 238
Scenario, Forecast [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Pre-tax gain on sale of common stock			$ 167
Scenario, Forecast [Member] | Yadkin [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds from sale of assets			$ 5
Alcoa Corporation [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Common stock outstanding percentage		80.10%
Number of common stock retained				36,311,767
Percentage of common stock retained				19.90%

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