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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.

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