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Note 13 - Retirement Plans and Other Postretirement Benefits (Details Textual) - USD ($)
$ in Millions
 3 Months Ended 12 Months Ended
Sep. 30, 2025
Jun. 30, 2025
Mar. 31, 2025
Sep. 30, 2025
Dec. 31, 2024
Defined Benefit Plan Disclosure [Line Items]          
Increase in discount rates     $ 22    
Remeasurement discount rate 5.03% 5.20% 5.26% 5.03% 5.45%
Remeasurement of teasury rate     4.59%   4.75%
Actuarial gain (Loss) $ 96 $ (16) $ (68)    
Actuarial loss associated with asset returns 20 56      
Partially offset by an asset actuarial gain (loss) (21) (8) 22    
Expected rate of return on plan assets assumption         5.20%
Settlement gain       $ 1  
KRIP's Projected Benefit Obligation ("PBO") [Member]          
Defined Benefit Plan Disclosure [Line Items]          
Actuarial gain (Loss) 76 40 (90)    
Partially offset by an asset actuarial gain (loss)     $ 22    
Mortality and Other Demographic Experience [Member]          
Defined Benefit Plan Disclosure [Line Items]          
Actuarial gain (Loss)   $ 48      
Termination Changes [Member]          
Defined Benefit Plan Disclosure [Line Items]          
Actuarial gain (Loss) 104        
Current Asset Class Allocation [Member]          
Defined Benefit Plan Disclosure [Line Items]          
Expected rate of return on plan assets assumption         3.80%
Demographic Experience [Member]          
Defined Benefit Plan Disclosure [Line Items]          
Partially offset by an asset actuarial gain (loss) $ 7