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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
Income Tax Disclosure [Abstract]
2021	$ 4
2022	7
2023	5
2024	4
2025	13
Thereafter	669
Total	$ 702	$ 612

X

- Definition

Deferred tax assets on tax loss carryforwards and investment credits expiration thereafter.

+ References

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- Definition

Deferred tax assets on tax loss carryforwards and investment credits expiration year five.

+ References

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- Definition

Deferred tax assets on tax loss carryforwards and investment credits expiration year four.

+ References

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- Definition

Deferred tax assets on tax loss carryforwards and investment credits expiration year one.

+ References

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- Definition

Deferred tax assets on tax loss carryforwards and investment credits expiration year three.

+ References

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- Definition

Deferred tax assets on tax loss carryforwards and investment credits expiration year two.

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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

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