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Accumulated Other Comprehensive Loss - Changes in Accumulated Other Comprehensive Loss by Component (Detail) - USD ($) $ in Millions | 3 Months Ended | 9 Months Ended
--- | --- | ---
Sep. 30, 2019 | Jun. 30, 2019 | Mar. 31, 2019 | Sep. 30, 2018 | Mar. 31, 2018 | Sep. 30, 2019 | Sep. 30, 2018
Accumulated Other Comprehensive Income (Loss) [Line Items] |  |  |  |  |  |  |  |
Beginning balance |  |  |  | $ (144) |  | $ (231) | $ (144) | $ (231)
Other comprehensive income (loss), before reclassifications, net of tax |  |  |  |  |  |  | (57) | 32
Amounts reclassified from accumulated other comprehensive loss: |  |  |  |  |  |  |  |
Amortization - prior service credit |  |  |  |  |  |  | (34) | (27)
Amortization - actuarial loss |  |  |  |  |  |  | 15 | 25
Amortization - settlement loss |  |  |  |  |  |  | 9 | 47
Other |  |  |  |  |  |  | (4) | (4)
Tax effect |  |  |  |  |  |  | 3 | (10)
Other comprehensive income (loss) |  | $ (51) | $ (10) | (7) | $ 65 | (2) | (68) | 63
Ending balance |  | (212) |  |  | (168) |  | (212) | (168)
Other comprehensive income (loss) before reclassifications, tax |  |  |  |  |  |  | (20) | 10
Accumulated Defined Benefit Plans Adjustment | Pension Benefits |  |  |  |  |  |  |  |
Accumulated Other Comprehensive Income (Loss) [Line Items] |  |  |  |  |  |  |  |
Beginning balance |  |  |  | (132) |  | (190) | (132) | (190)
Other comprehensive income (loss), before reclassifications, net of tax |  |  |  |  |  |  | (58) | 35
Amounts reclassified from accumulated other comprehensive loss: |  |  |  |  |  |  |  |
Amortization - prior service credit | [1] |  |  |  |  |  | (34) | (25)
Amortization - actuarial loss | [1] |  |  |  |  |  | 16 | 26
Amortization - settlement loss | [1] |  |  |  |  |  | 9 | 47
Tax effect |  |  |  |  |  |  | 2 | (12)
Other comprehensive income (loss) |  |  |  |  |  |  | (65) | 71
Ending balance |  | (197) |  |  | (119) |  | (197) | (119)
Accumulated Defined Benefit Plans Adjustment | Other Benefits |  |  |  |  |  |  |  |
Accumulated Other Comprehensive Income (Loss) [Line Items] |  |  |  |  |  |  |  |
Beginning balance |  |  |  | (23) |  | (48) | (23) | (48)
Other comprehensive income (loss), before reclassifications, net of tax |  |  |  |  |  |  | 1 | (1)
Amounts reclassified from accumulated other comprehensive loss: |  |  |  |  |  |  |  |
Amortization - prior service credit | [1] |  |  |  |  |  | 0 | (2)
Amortization - actuarial loss | [1] |  |  |  |  |  | (1) | (1)
Amortization - settlement loss |  |  |  |  |  |  | 0 | 0
Tax effect |  |  |  |  |  |  | 0 | 1
Other comprehensive income (loss) |  |  |  |  |  |  | 0 | (3)
Ending balance |  | (23) |  |  | (51) |  | (23) | (51)
Gain on Cash Flow Hedge |  |  |  |  |  |  |  |
Accumulated Other Comprehensive Income (Loss) [Line Items] |  |  |  |  |  |  |  |
Beginning balance |  |  |  | 2 |  | 4 | 2 | 4
Other comprehensive income (loss), before reclassifications, net of tax |  |  |  |  |  |  | 0 | (2)
Amounts reclassified from accumulated other comprehensive loss: |  |  |  |  |  |  |  |
Tax effect |  |  |  |  |  |  | 0 | 0
Other comprehensive income (loss) |  |  |  |  |  |  | 0 | (2)
Ending balance |  | 2 |  |  | 2 |  | 2 | 2
Workers Compensation |  |  |  |  |  |  |  |
Accumulated Other Comprehensive Income (Loss) [Line Items] |  |  |  |  |  |  |  |
Beginning balance |  |  |  | $ 9 |  | $ 3 | 9 | 3
Other comprehensive income (loss), before reclassifications, net of tax |  |  |  |  |  |  | 0 | 0
Amounts reclassified from accumulated other comprehensive loss: |  |  |  |  |  |  |  |
Other |  |  |  |  |  |  | (4) | (4)
Tax effect |  |  |  |  |  |  | 1 | 1
Other comprehensive income (loss) |  |  |  |  |  |  | (3) | (3)
Ending balance |  | $ 6 |  |  | $ 0 |  | $ 6 | $ 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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- Definition Accumulated change in equity from transactions and other events and circumstances from non-owner sources, net of tax effect, at period end. Excludes Net Income (Loss), and accumulated changes in equity from transactions resulting from investments by owners and distributions to owners. Includes foreign currency translation items, certain pension adjustments, unrealized gains and losses on certain investments in debt and equity securities, other than temporary impairment (OTTI) losses related to factors other than credit losses on available-for-sale and held-to-maturity debt securities that an entity does not intend to sell and it is not more likely than not that the entity will be required to sell before recovery of the amortized cost basis, as well as changes in the fair value of derivatives related to the effective portion of a designated cash flow hedge. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 11 -URI http://asc.fasb.org/extlink&oid=118930883&loc=d3e637-108580 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 14A -URI http://asc.fasb.org/extlink&oid=118930883&loc=SL7669686-108580 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 14 -URI http://asc.fasb.org/extlink&oid=118930883&loc=d3e681-108580 + Details
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- Definition Amount after tax, before reclassification adjustments of other comprehensive income (loss). + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 14A -URI http://asc.fasb.org/extlink&oid=118930883&loc=SL7669686-108580 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 55 -Paragraph 15 -URI http://asc.fasb.org/extlink&oid=118951672&loc=d3e1436-108581 + Details
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