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Fair Value Measurements (Details) - USD ($)
$ in Millions
Sep. 30, 2025
Dec. 31, 2024
Schedule of Investments [Line Items]    
Cash $ 439 $ 168
Cash and Cash Equivalents    
Cash equivalents:    
Cost Basis 1,838 1,614
Unrealized Gains 0 0
Unrealized Losses 0 0
Fair Value 1,838 1,614
U.S. and Canadian government obligations | Cash and Cash Equivalents    
Cash equivalents:    
Cost Basis 366 932
Unrealized Gains 0 0
Unrealized Losses 0 0
Fair Value 366 932
Other debt securities | Cash and Cash Equivalents    
Cash equivalents:    
Cost Basis 1,033 514
Unrealized Gains 0 0
Unrealized Losses 0 0
Fair Value 1,033 514
Nonqualified employee benefit trusts    
Cash equivalents:    
Cost Basis 15 15
Unrealized Gains 3 2
Unrealized Losses 0 0
Fair Value $ 18 $ 17