Fair Value Measurement - Equity Securities Without Readily Determinable Fair Value (Details) shares in Millions, $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2019 USD ($) shares	Jun. 30, 2018 USD ($)	Jun. 30, 2019 USD ($) shares	Jun. 30, 2018 USD ($)	Dec. 31, 2018 USD ($)
Fair Value Disclosures [Abstract]
Carrying value	$ 1,704	$ 1,471	$ 1,704	$ 1,471	$ 1,500
Upward carrying value changes	52	67	136	562
Downward carrying value changes/impairment	(36)	$ (26)	(42)	$ (28)
Cumulative upward carrying value changes	446		446
Cumulative downward carrying value changes/impairment	$ (202)		$ (202)
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

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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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Amount of cumulative 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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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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Amount of cumulative 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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