Income Tax - Gross Deferred Tax Assets on Tax Loss Carryforwards and Investment Credits Expiration (Detail) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
2017	$ 16
2018	89
2019	80
2020	16
2021	3
Thereafter	600
Total	$ 804	$ 827

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

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- Definition

Deferred Tax Assets On Tax Loss Carryforwards And Investment Credits Expiration Year Five

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- Definition

Deferred tax assets on tax loss carryforwards and investment credits expiration Year Four.

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- Definition

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

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No definition available.

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- Definition

Deferred tax assets on tax loss carryforwards and investment credits expiration Year Three.

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- Definition

Deferred tax assets on tax loss carryforwards and investment credits expiration Year Two.

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No definition available.

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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://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 25
-Paragraph 20
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=68052875&loc=d3e28680-109314

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 6
-URI http://asc.fasb.org/extlink&oid=65882285&loc=d3e32621-109319

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=65882285&loc=d3e32632-109319

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