v3.26.1
Accumulated Other Comprehensive Income (Loss), Net of Tax - Schedule of Reclassifications Out of Accumulated Other Comprehensive Income (Details) - USD ($)
$ in Millions
3 Months Ended 12 Months Ended
Mar. 31, 2026
Mar. 31, 2025
Dec. 31, 2025
Reclassification out of Accumulated Other Comprehensive Income [Line Items]      
Reclassification from Accumulated Other Comprehensive Income, Current Period, before Tax $ (21) $ (2)  
Reclassification from Accumulated Other Comprehensive Income, Current Period, Tax 9 0  
Amounts Reclassified from Accumulated Other Comprehensive Income (Loss) (12) (2)  
Cash Flow Hedges [Member]      
Reclassification out of Accumulated Other Comprehensive Income [Line Items]      
Cash Flow Hedge, Pre-tax 1 1  
Cash Flow Hedge, Tax 0 (1)  
Cash Flow Hedge, After Tax 1 0  
Reclassification from Accumulated Other Comprehensive Income, Current Period, before Tax 1   $ 5
Amounts Reclassified from Accumulated Other Comprehensive Income (Loss) 1 0 $ 4
Pension and OPEB Plans [Member]      
Reclassification out of Accumulated Other Comprehensive Income [Line Items]      
Reclassification Adjustment from AOCI, Pension and OPEB, Pre-Tax (2) (2)  
Reclassification Adjustment from AOCI, Pension and OPEB, Tax 1 1  
Reclassification Adjustment from AOCI, Pension and OPEB, After-Tax (1) (1)  
Amounts Reclassified from Accumulated Other Comprehensive Income (Loss) (1) (1)  
Available-for-Sale Securities [Member]      
Reclassification out of Accumulated Other Comprehensive Income [Line Items]      
Reclassification for Available for Sale Debt Securities, Pre-Tax (20) (1)  
Reclassification for Available for Sale Debt Securities, Tax 8 0  
Reclassification for Available for Sale Debt Securities, After-Tax (12) (1)  
Amounts Reclassified from Accumulated Other Comprehensive Income (Loss) (12) (1)  
Interest Expense [Member] | Cash Flow Hedges [Member]      
Reclassification out of Accumulated Other Comprehensive Income [Line Items]      
Cash Flow Hedge, Pre-tax 1 1  
Cash Flow Hedge, Tax 0 (1)  
Cash Flow Hedge, After Tax 1 0  
Non-Operating Pension and OPEB Credits (Costs) [Member] | Pension and OPEB Plans [Member]      
Reclassification out of Accumulated Other Comprehensive Income [Line Items]      
Amortization of Net Actuarial Loss, Pre-Tax (2) (2)  
Amortization of Net Actuarial Loss, Tax 1 1  
Amortization of Net Actuarial Loss, After-Tax (1) (1)  
Net Gains (Losses) on Trust Investments [Member] | Available-for-Sale Securities [Member]      
Reclassification out of Accumulated Other Comprehensive Income [Line Items]      
Reclassification for Available for Sale Debt Securities, Pre-Tax (20) (1)  
Reclassification for Available for Sale Debt Securities, Tax 8 0  
Reclassification for Available for Sale Debt Securities, After-Tax $ (12) $ (1)