v3.26.1
Accumulated Other Comprehensive Income (Loss) (Changes in Accumulated Other Comprehensive Loss by Component) (Detail) - USD ($)
$ in Millions
 3 Months Ended 6 Months Ended
Jun. 30, 2026
Mar. 31, 2026
Jun. 30, 2025
Mar. 31, 2025
Jun. 30, 2026
Jun. 30, 2025
Accumulated Other Comprehensive Income (Loss) [Line Items]            
Accumulated other comprehensive (income) loss, other, after tax, beginning balance $ (1) $ (1) $ (1) $ (1) $ (1) $ (1)
Accumulated other comprehensive loss, beginning balance (108) (105) (109) (114) (105) (114)
Other comprehensive income (loss), before reclassifications, net of tax 1 (1) 2 8    
Amounts reclassified from accumulated other comprehensive loss:            
Amortization of prior service credit (9) (7) (7) (8)    
Amortization of actuarial loss 5 4 4 4    
Settlement loss     1      
Other     1      
Tax effect 1 1 0 1    
Other comprehensive income (loss) (2) (3) 1 5 (5) 6
Accumulated other comprehensive (income) loss, other, after tax, ending balance (1) (1) 0 (1) (1) 0
Accumulated other comprehensive loss, ending balance (110) (108) (108) (109) (110) (108)
Other comprehensive income (loss) before reclassifications, tax 1 0   2    
Pension Benefits            
Accumulated Other Comprehensive Income (Loss) [Line Items]            
Accumulated other comprehensive (income) loss, defined benefit plan, after tax, beginning balance (207) (209) (228) (235) (209) (235)
Amounts reclassified from accumulated other comprehensive loss:            
Accumulated other comprehensive (income) loss, defined benefit plan, after tax, ending balance (205) (207) (224) (228) (205) (224)
Other Benefits            
Accumulated Other Comprehensive Income (Loss) [Line Items]            
Accumulated other comprehensive (income) loss, defined benefit plan, after tax, beginning balance 100 105 120 122 105 122
Amounts reclassified from accumulated other comprehensive loss:            
Accumulated other comprehensive (income) loss, defined benefit plan, after tax, ending balance 96 100 116 120 $ 96 $ 116
Accumulated Defined Benefit Plans Adjustment | Pension Benefits            
Accumulated Other Comprehensive Income (Loss) [Line Items]            
Other comprehensive income (loss), before reclassifications, net of tax 1 0 3 5    
Amounts reclassified from accumulated other comprehensive loss:            
Amortization of prior service credit [1] (3) (2) (2) (2)    
Amortization of actuarial loss [1] 5 4 4 4    
Settlement loss [1]     1      
Other [1]     0      
Tax effect (1) 0 (2) 0    
Other comprehensive income (loss) 2 2 4 7    
Accumulated Defined Benefit Plans Adjustment | Other Benefits            
Accumulated Other Comprehensive Income (Loss) [Line Items]            
Other comprehensive income (loss), before reclassifications, net of tax 0 (1) (1) 3    
Amounts reclassified from accumulated other comprehensive loss:            
Amortization of prior service credit [1] (6) (5) (5) (6)    
Amortization of actuarial loss [1] 0 0 0 0    
Settlement loss     0      
Other     0      
Tax effect 2 1 2 1    
Other comprehensive income (loss) (4) (5) (4) (2)    
Other            
Accumulated Other Comprehensive Income (Loss) [Line Items]            
Other comprehensive income (loss), before reclassifications, net of tax 0 0 0 0    
Amounts reclassified from accumulated other comprehensive loss:            
Amortization of prior service credit 0 0 0 0    
Amortization of actuarial loss 0 0 0 0    
Settlement loss     0      
Other     1      
Tax effect 0 0 0 0    
Other comprehensive income (loss) $ 0 $ 0 $ 1 $ 0    
[1] These accumulated other comprehensive loss components are included in the computation of net periodic benefit cost. See Note 21.