Derivative Instruments and Other Financial Instruments Used For Hedging - Gain or (Loss) Recognized in Income on Derivative Instruments (Details) - Trading derivatives - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2019	Mar. 31, 2018
Trading Derivatives
Trading account activities	$ (20)	$ 139
Interest rate derivative contracts
Trading Derivatives
Trading account activities	(35)	113
Equity contracts
Trading Derivatives
Trading account activities	4	17
Foreign exchange derivative contracts
Trading Derivatives
Trading account activities	$ 11	$ 9

Amount of gain (loss) resulting from the difference between the acquisition price and the selling price or fair value of trading assets and trading liabilities, conducted separately from customer trading activities. Includes, but is not limited to, changes in fair value of trading assets and trading liabilities.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 225
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-04.13(e))
-URI http://asc.fasb.org/extlink&oid=6879574&loc=d3e536633-122882

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 940
-SubTopic 320
-Section 35
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=35711043&loc=d3e42454-110968

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 940
-SubTopic 320
-Section 45
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=35711157&loc=d3e42567-110969

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4F
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5624186-113959

Name:	us-gaap_TradingGainsLosses
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration