Investments - Carrying Value of Equity Investments Without Readily Determinable Fair Values (Details) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2018 USD ($)	Sep. 30, 2018 USD ($)
Equity Securities without Readily Determinable Fair Value [Roll Forward]
Carrying value, beginning of period	$ 859	$ 872
Additions	0	23
Sales	(718)	(718)
Downward adjustments for observable price changes and impairment	0	(20)
Foreign currency translation and other	(3)	(19)
Carrying value, end of period	138	138
Cumulative downward adjustments for price changes and impairment	$ 81	$ 81

Equity Securities without Readily Determinable Fair Value, Additions

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Equity Securities without Readily Determinable Fair Value, Foreign Currency Translation

+ References

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- Definition

Equity Securities without Readily Determinable Fair Value [Roll Forward]

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Equity Securities without Readily Determinable Fair Value, Sales

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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 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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