Investments - Unrealized gains (losses) recognized in income (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Consolidated Entity Excluding Variable Interest Entities (VIE)
Gain (Loss) on Securities [Line Items]
Debt Securities, Trading, Unrealized Gain (Loss)	$ 98	$ (41)	$ 169	$ (110)
Equity Securities, FV-NI, Unrealized Gain (Loss)	2	4	20	4
Related Party \| Consolidated Entity Excluding Variable Interest Entities (VIE)
Gain (Loss) on Securities [Line Items]
Debt Securities, Trading, Unrealized Gain (Loss)	(13)	(4)	(16)	(6)
Equity Securities, FV-NI, Unrealized Gain (Loss)	(3)	0	0	0
Variable Interest Entities \| Related Party
Gain (Loss) on Securities [Line Items]
Debt Securities, Trading, Unrealized Gain (Loss)	0	1	1	1
Equity Securities, FV-NI, Unrealized Gain (Loss)	$ (2)	$ (14)	$ (2)	$ (39)

Amount of unrealized gain (loss) on investment in debt security measured at fair value with change in fair value recognized in net income (trading).

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 9
-Subparagraph (e)
-URI http://asc.fasb.org/extlink&oid=118939692&loc=d3e27357-111563

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Amount of unrealized gain (loss) on investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI).

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 321
-SubTopic 10
-Section 50
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=116654751&loc=SL75117546-209714

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