v3.26.3
Accumulated Other Comprehensive Income (Loss) (Changes in Accumulated Other Comprehensive Loss by Component) (Detail) - USD ($)
$ in Millions
 3 Months Ended 9 Months Ended
Sep. 30, 2026
Jun. 30, 2026
Mar. 31, 2026
Sep. 30, 2025
Jun. 30, 2025
Mar. 31, 2025
Sep. 30, 2026
Sep. 30, 2025
Accumulated Other Comprehensive Income (Loss) [Line Items]                
Accumulated other comprehensive (income) loss, other, after tax, beginning balance $ (1) $ (1) $ (1) $ 0 $ (1) $ (1) $ (1) $ (1)
Accumulated other comprehensive loss, beginning balance (110) (108) (105) (108) (109) (114) (105) (114)
Other comprehensive income (loss), before reclassifications, net of tax (1) 1 (1) 1 2 8    
Amounts reclassified from accumulated other comprehensive loss:                
Amortization of prior service credit (7) (9) (7) (7) (7) (8)    
Amortization of actuarial loss 3 5 4 4 4 4    
Settlement loss (1)       1      
Other         1      
Tax effect 1 1 1 1 0 1    
Other comprehensive income (loss) (5) (2) (3) (1) 1 5 (10) 5
Accumulated other comprehensive (income) loss, other, after tax, ending balance (1) (1) (1) 0 0 (1) (1) 0
Accumulated other comprehensive loss, ending balance (115) (110) (108) (109) (108) (109) (115) (109)
Other comprehensive income (loss) before reclassifications, tax 0 0 0 1 1 2    
Pension Benefits                
Accumulated Other Comprehensive Income (Loss) [Line Items]                
Accumulated other comprehensive (income) loss, defined benefit plan, after tax, beginning balance (205) (207) (209) (224) (228) (235) (209) (235)
Amounts reclassified from accumulated other comprehensive loss:                
Accumulated other comprehensive (income) loss, defined benefit plan, after tax, ending balance (206) (205) (207) (221) (224) (228) (206) (221)
Other Benefits                
Accumulated Other Comprehensive Income (Loss) [Line Items]                
Accumulated other comprehensive (income) loss, defined benefit plan, after tax, beginning balance 96 100 105 116 120 122 105 122
Amounts reclassified from accumulated other comprehensive loss:                
Accumulated other comprehensive (income) loss, defined benefit plan, after tax, ending balance 92 96 100 112 116 120 $ 92 $ 112
Accumulated Defined Benefit Plans Adjustment | Pension Benefits                
Accumulated Other Comprehensive Income (Loss) [Line Items]                
Other comprehensive income (loss), before reclassifications, net of tax (1) 1 0 1 3 5    
Amounts reclassified from accumulated other comprehensive loss:                
Amortization of prior service credit [1] (2) (3) (2) (2) (2) (2)    
Amortization of actuarial loss [1] 3 5 4 4 4 4    
Settlement loss [1] (1)       1      
Other [1]         0      
Tax effect 0 (1) 0 0 (2) 0    
Other comprehensive income (loss) (1) 2 2 3 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 0 (1) 0 (1) 3    
Amounts reclassified from accumulated other comprehensive loss:                
Amortization of prior service credit [1] (5) (6) (5) (5) (5) (6)    
Amortization of actuarial loss [1] 0 0 0 0 0 0    
Settlement loss 0       0      
Other         0      
Tax effect 1 2 1 1 2 1    
Other comprehensive income (loss) (4) (4) (5) (4) (4) (2)    
Other                
Accumulated Other Comprehensive Income (Loss) [Line Items]                
Other comprehensive income (loss), before reclassifications, net of tax 0 0 0 0 0 0    
Amounts reclassified from accumulated other comprehensive loss:                
Amortization of prior service credit 0 0 0 0 0 0    
Amortization of actuarial loss 0 0 0 0 0 0    
Settlement loss 0       0      
Other         1      
Tax effect 0 0 0 0 0 0    
Other comprehensive income (loss) $ 0 $ 0 $ 0 $ 0 $ 1 $ 0    
[1] These accumulated other comprehensive loss components are included in the computation of net periodic benefit cost. See Note 22.