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