Restructuring and Other Charges - Narrative (Details) $ in Millions	3 Months Ended				6 Months Ended	9 Months Ended
	Mar. 31, 2022 USD ($)	Sep. 30, 2021 USD ($)	Sep. 30, 2020 USD ($) employee	Mar. 31, 2020 USD ($)	Jun. 30, 2021 employee	Sep. 30, 2021 USD ($) employee	Sep. 30, 2020 USD ($) employee
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges (E)		$ 14	$ 3			$ 612	$ 61
Cash payments, restructuring				$ 27		11
One-time Termination Benefits
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges (E)		5				573
Other miscellaneous costs
Restructuring Cost and Reserve [Line Items]
Cash payments, restructuring				3		2
Layoff costs
Restructuring Cost and Reserve [Line Items]
Cash payments, restructuring				$ 24		9
Spin-off
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges (E)							2
2019 Restructuring Program [Member] | Layoff costs
Restructuring Cost and Reserve [Line Items]
Cash payments, restructuring		1				$ 3
2020 Restructuring Programs
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges (E)			$ 3				$ 61
Number of employees separated | employee						485
Expected number of employees separated | employee			450		550	500
Restructuring and Related Cost, Change in Expected Positions Eliminated | employee			130
2020 Restructuring Programs | Building and Construction System and Extrustions [Member]
Restructuring Cost and Reserve [Line Items]
Expected number of employees separated | employee							140
2020 Restructuring Programs | COVID-19
Restructuring Cost and Reserve [Line Items]
Expected number of employees separated | employee							440
2020 Restructuring Programs | COVID-19 | Extrusions
Restructuring Cost and Reserve [Line Items]
Expected number of employees separated | employee			30
2020 Restructuring Programs | One-time Termination Benefits
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges (E)			$ 3				$ 58
2020 Restructuring Programs | Disposals | Hard Alloy Extrusions Plant In South Korea And Aluminum Rolling Mill In Brazil
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges (E)							(25)
2020 Restructuring Programs | Reversal of Reserve [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges (E)			(2)			$ 2	(14)
2020 Restructuring Programs | Reversal of Reserve [Member] | Forecast
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges (E)	$ 8
2020 Restructuring Programs | Other miscellaneous costs
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges (E)			1				7
2020 Restructuring Programs | Layoff costs
Restructuring Cost and Reserve [Line Items]
Cash payments, restructuring		1				4
2020 Restructuring Programs | Layoff costs | Building and Construction System and Extrustions [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges (E)							8
2020 Restructuring Programs | Layoff costs | COVID-19
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges (E)							18
2020 Restructuring Programs | Layoff costs | COVID-19 | Extrusions
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges (E)			$ 1
2020 Restructuring Programs | Reversal Of Reserve, Environmental Matter
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges (E)							(5)
2020 Restructuring Programs | Facility Closing | Building and Construction System and Extrustions [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges (E)							11
2020 Restructuring Programs | Legacy Non-Income Tax Matters
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges (E)							4
2020 Restructuring Programs | Spin-off
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges (E)							$ 2
2021 Restructuring Programs
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges (E)		14				$ 612
2021 Restructuring Programs | Extrusions
Restructuring Cost and Reserve [Line Items]
Number of employees separated | employee						115
2021 Restructuring Programs | One-time Termination Benefits
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges (E)		5				$ 573
2021 Restructuring Programs | Disposals | Aluminum Rolling Mill in Itapissuma, Brazil
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges (E)						1
2021 Restructuring Programs | Idling of Operations | Extrusions
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges (E)		3				6
2021 Restructuring Programs | Reversal of Reserve [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges (E)		1				3
2021 Restructuring Programs | Legal Matters, Other
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges (E)		3				3
2021 Restructuring Programs | Other miscellaneous costs
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges (E)		1				2
2021 Restructuring Programs | Layoff costs
Restructuring Cost and Reserve [Line Items]
Cash payments, restructuring		1				2
2021 Restructuring Programs | Facility Closing
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges (E)						34
2021 Restructuring Programs | Legacy Tax Matters
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges (E)		$ 3				$ 4