v3.26.1
Debt - Description of fair value adjustments for guaranteed notes (Details) - USD ($)
$ in Millions
 3 Months Ended 6 Months Ended
Jun. 30, 2026
Jun. 30, 2025
Jun. 30, 2026
Jun. 30, 2025
Dec. 31, 2025
Debt Instrument [Line Items]          
Gains (Losses) $ 2 $ (20) $ 6 $ (45)  
Cumulative Fair Value Hedging Adjustments Included in Carrying Amount of Debt 79   79   $ 73
Guaranteed Notes due 2025, 1.25%          
Debt Instrument [Line Items]          
Gains (Losses) 0 (1) 0 (3)  
Cumulative Fair Value Hedging Adjustments Included in Carrying Amount of Debt $ 0   $ 0   0
Guaranteed Notes due 2025, 1.25% | Issued by LYB International Finance III LLC:          
Debt Instrument [Line Items]          
Stated interest rate (in percent) 1.25%   1.25%    
Guaranteed Notes due 2026, 0.875%          
Debt Instrument [Line Items]          
Gains (Losses) $ (1) (1) $ (1) (1)  
Cumulative Fair Value Hedging Adjustments Included in Carrying Amount of Debt $ 1   $ 1   2
Guaranteed Notes due 2026, 0.875% | Issued by LYB International Finance II B.V.:          
Debt Instrument [Line Items]          
Stated interest rate (in percent) 0.875%   0.875%    
Guaranteed Notes due 2027, 3.5%          
Debt Instrument [Line Items]          
Gains (Losses) $ 0 (1) $ 1 (3)  
Cumulative Fair Value Hedging Adjustments Included in Carrying Amount of Debt $ 1   $ 1   0
Guaranteed Notes due 2027, 3.5% | Issued by LYB International Finance II B.V.:          
Debt Instrument [Line Items]          
Stated interest rate (in percent) 3.50%   3.50%    
Guaranteed Notes due 2030, 3.375%          
Debt Instrument [Line Items]          
Gains (Losses) $ 0 (2) $ 0 (5)  
Cumulative Fair Value Hedging Adjustments Included in Carrying Amount of Debt $ (2)   $ (2)   (2)
Guaranteed Notes due 2030, 3.375% | Issued by LYB International Finance III LLC:          
Debt Instrument [Line Items]          
Stated interest rate (in percent) 3.375%   3.375%    
Guaranteed Notes due 2030, 2.25%          
Debt Instrument [Line Items]          
Gains (Losses) $ 1 (2) $ 1 (5)  
Cumulative Fair Value Hedging Adjustments Included in Carrying Amount of Debt $ 15   $ 15   14
Guaranteed Notes due 2030, 2.25% | Issued by LYB International Finance III LLC:          
Debt Instrument [Line Items]          
Stated interest rate (in percent) 2.25%   2.25%    
Guaranteed Notes due 2031, 1.625%          
Debt Instrument [Line Items]          
Gains (Losses) $ (1) (1) $ 0 1  
Cumulative Fair Value Hedging Adjustments Included in Carrying Amount of Debt $ 5   $ 5   5
Guaranteed Notes due 2031, 1.625% | Issued by LYB International Finance II B.V.:          
Debt Instrument [Line Items]          
Stated interest rate (in percent) 1.625%   1.625%    
Guaranteed Notes due 2050, 4.2%          
Debt Instrument [Line Items]          
Gains (Losses) $ 1 (1) $ 1 (2)  
Cumulative Fair Value Hedging Adjustments Included in Carrying Amount of Debt $ 14   $ 14   13
Guaranteed Notes due 2050, 4.2% | Issued by LYB International Finance III LLC:          
Debt Instrument [Line Items]          
Stated interest rate (in percent) 4.20%   4.20%    
Guaranteed Notes due 2051, 3.625%          
Debt Instrument [Line Items]          
Gains (Losses) $ 1 (9) $ 2 (23)  
Cumulative Fair Value Hedging Adjustments Included in Carrying Amount of Debt $ 39   $ 39   37
Guaranteed Notes due 2051, 3.625% | Issued by LYB International Finance III LLC:          
Debt Instrument [Line Items]          
Stated interest rate (in percent) 3.625%   3.625%    
Guaranteed Notes due 2060, 3.8%          
Debt Instrument [Line Items]          
Gains (Losses) $ 1 $ (2) $ 2 $ (4)  
Cumulative Fair Value Hedging Adjustments Included in Carrying Amount of Debt $ 6   $ 6   $ 4
Guaranteed Notes due 2060, 3.8% | Issued by LYB International Finance III LLC:          
Debt Instrument [Line Items]          
Stated interest rate (in percent) 3.80%   3.80%