Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	$ 3,577	$ 4,605	$ 5,569
Other comprehensive income (loss):
Tax expense			(1)
Total Other comprehensive income (loss), net of tax	80	16	(401)
Ending balance	3,508	3,577	4,605
Cumulative Effect, Period of Adoption, Adjustment
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance			73
Accumulated other comprehensive loss balance at end of period
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(1,943)	(3,329)	(2,926)
Other comprehensive income (loss):
Total Other comprehensive income (loss), net of tax	80	16	(401)
Ending balance	(1,863)	(1,943)	(3,329)
Accumulated other comprehensive loss balance at end of period | Cumulative Effect, Period of Adoption, Adjustment
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance			(2)
Pension and other postretirement benefits (H)
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(980)	(2,732)	(2,344)
Other comprehensive income (loss):
Unrecognized net actuarial gain (loss) and prior service cost/benefit	111	(211)	(587)
Tax (expense) benefit	(26)	48	129
Total Other comprehensive income (loss) before reclassifications, net of tax	85	(163)	(458)
Amortization of net actuarial loss and prior service cost	123	149	90
Tax expense	(27)	(32)	(20)
Total amount reclassified from Accumulated other comprehensive loss, net of tax	96	117	70
Total Other comprehensive income (loss), net of tax	181	(46)	(388)
Transfer to Arconic Corporation	0	1,798	0
Ending balance	(799)	(980)	(2,732)
Foreign currency translation
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(966)	(596)	(583)
Other comprehensive income (loss):
Total Other comprehensive income (loss) before reclassifications, net of tax	(96)	58	(13)
Transfer to Arconic Corporation	0	(428)	0
Ending balance	(1,062)	(966)	(596)
Debt securities
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	0	0	(3)
Other comprehensive income (loss):
Total Other comprehensive income (loss) before reclassifications, net of tax	0	0	3
Ending balance	0	0	0
Cash flow hedges
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	3	(1)	4
Other comprehensive income (loss):
Unrecognized net actuarial gain (loss) and prior service cost/benefit	20	0	(9)
Tax (expense) benefit	(4)	0	3
Total Other comprehensive income (loss) before reclassifications, net of tax	16	0	(6)
Amortization of net actuarial loss and prior service cost	(26)	6	4
Tax expense	5	(2)
Total amount reclassified from Accumulated other comprehensive loss, net of tax	(21)	4	3
Total Other comprehensive income (loss), net of tax	(5)	4	(3)
Ending balance	$ (2)	$ 3	(1)
Cash flow hedges | Cumulative Effect, Period of Adoption, Adjustment
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance			$ (2)