Debt - Notes payable and bank lines (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Uncommitted and committed bank lines
Debt
Weighted average interest rate (as a percent)	7.34%	7.03%
Uncommitted bank lines
Debt
Lines of credit	$ 150	$ 326
Compensating balance	5
Uncommitted bank lines | Denominated in foreign currencies
Debt
Lines of credit	70	194
Uncommitted bank lines | South African Rand
Debt
Lines of credit	57	174
Committed bank lines
Debt
Lines of credit	105	$ 131
Maximum capacity	$ 450