Fair Value Measurement - Equity Securities Without Readily Determinable Fair Value (Details) shares in Millions, $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2018 USD ($) shares	Sep. 30, 2018 USD ($) shares
Fair Value Disclosures [Abstract]
Carrying value	$ 1,801	$ 1,801
Upward carrying value changes	14	540
Downward carrying value changes/impairment	$ (127)	$ (156)
Common stock \| Class B \| VISA
Investment Holdings [Line Items]
Interest owned, included in other assets (in shares) \| shares	40	40
Conversion rate	1.6298	1.6298

Conversion of Stock, Conversion Rate

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Equity Securities without Readily Determinable Fair Value, Shares

+ References

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- Definition

Amount of investment in equity security without readily determinable fair value.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 321
-SubTopic 10
-Section 50
-Paragraph 3
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=84241550&loc=SL75117539-209714

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- Definition

Amount of loss from downward price adjustment on investment in equity security without readily determinable fair value.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 321
-SubTopic 10
-Section 50
-Paragraph 3
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=84241550&loc=SL75117539-209714

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- Definition

Amount of gain from upward price adjustment on investment in equity security without readily determinable fair value.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 321
-SubTopic 10
-Section 50
-Paragraph 3
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=84241550&loc=SL75117539-209714

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