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Fair Value Measurements (Details) - USD ($)
$ in Millions
Sep. 30, 2024
Dec. 31, 2023
Schedule of Investments [Line Items]    
Cash $ 331 $ 208
Cash and Cash Equivalents    
Cash equivalents:    
Cost Basis 1,877 2,032
Unrealized Gains 0 0
Unrealized Losses 0 0
Fair Value 1,877 2,032
U.S. and Canadian government obligations | Cash and Cash Equivalents    
Cash equivalents:    
Cost Basis 1,045 1,488
Unrealized Gains 0 0
Unrealized Losses 0 0
Fair Value 1,045 1,488
Other debt securities | Cash and Cash Equivalents    
Cash equivalents:    
Cost Basis 501 336
Unrealized Gains 0 0
Unrealized Losses 0 0
Fair Value 501 336
Nonqualified employee benefit trusts    
Cash equivalents:    
Cost Basis 15 16
Unrealized Gains 3 1
Unrealized Losses 0 0
Fair Value $ 18 $ 17