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Income Tax - Gross Deferred Tax Assets on Tax Loss Carryforwards and Investment Credits Expiration (Detail) - USD ($) $ in Millions | Dec. 31, 2020 | Dec. 31, 2019
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Income Tax Disclosure [Abstract] |  |
2021 | $ 4 |
2022 | 7 |
2023 | 5 |
2024 | 4 |
2025 | 13 |
Thereafter | 669 |
Total | $ 702 | $ 612

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- Definition Amount before allocation of valuation allowances of deferred tax asset attributable to deductible operating loss carryforwards. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 8 -URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32632-109319 Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 6 -URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32621-109319 + Details
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