Balance Sheet and Cash Flow Supplemental Information - Schedule of Additional Supplemental Cash Flow Information (Details) - USD ($) $ in Millions |
9 Months Ended | 12 Months Ended | |
|---|---|---|---|
Sep. 30, 2026 |
Sep. 30, 2025 |
Dec. 31, 2025 |
|
| Supplemental non cash information: | |||
| Operating activities - Chloride slag inventory purchases made from AMIC (including VAT) | $ 0 | $ 11 | |
| Operating activities - MGT sales made to ATTM | 5 | 5 | |
| Investing activities - In-kind receipt of AMIC loan repayment | 0 | 11 | |
| Financing activities - Initial commercial insurance premium financing agreement | 17 | 21 | |
| Financing activities - Repayment of MGT loan | 5 | $ 5 | |
| Capital expenditures acquired but not yet paid | $ 37 | $ 44 | |