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Merger Agreement (Details) - USD ($)
$ / shares in Units, $ in Millions
3 Months Ended 9 Months Ended
Jul. 31, 2025
Sep. 30, 2025
Sep. 30, 2024
Sep. 30, 2025
Sep. 30, 2024
Dec. 31, 2024
Business Combination [Line Items]            
Common stock, par or stated value per share (in dollars per share) $ 1.00 $ 1.00   $ 1.00   $ 1.00
Merger-related expenses   $ 15 $ 0 $ 15 $ 0  
Union Pacific Merger            
Business Combination [Line Items]            
Merger-related expenses   $ 15   $ 15    
Union Pacific Merger | Union Pacific            
Business Combination [Line Items]            
Common stock, par or stated value per share (in dollars per share) $ 2.50          
Business combination, consideration transferred, shares issued per acquiree share 1          
Business combination, consideration transferred, shares issued per acquiree share (in dollars per share) $ 88.82          
Specified termination fee $ 2,500          
Union Pacific Merger | Norfolk Southern            
Business Combination [Line Items]            
Specified termination fee $ 2,500