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Fair Value Measurements (Details) - USD ($)
$ in Millions
Sep. 30, 2023
Dec. 31, 2022
Schedule of Investments [Line Items]    
Cash $ 193 $ 153
Cash and Cash Equivalents    
Cash equivalents:    
Cost Basis 3,254 2,323
Unrealized Gains 0 0
Unrealized Losses 0 0
Fair Value 3,254 2,323
U.S. and Canadian government obligations | Cash and Cash Equivalents    
Cash equivalents:    
Cost Basis 2,687 1,902
Unrealized Gains 0 0
Unrealized Losses 0 0
Fair Value 2,687 1,902
Other debt securities | Cash and Cash Equivalents    
Cash equivalents:    
Cost Basis 374 268
Unrealized Gains 0 0
Unrealized Losses 0 0
Fair Value 374 268
Nonqualified employee benefit trusts    
Cash equivalents:    
Cost Basis 16 16
Unrealized Gains 0 0
Unrealized Losses 0 0
Fair Value $ 16 $ 16