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, 2020	Mar. 31, 2019
Trading Derivatives
Trading account activities	$ (37)	$ (20)
Interest rate derivative contracts
Trading Derivatives
Trading account activities	(59)	(35)
Equity contracts
Trading Derivatives
Trading account activities	4	4
Foreign exchange derivative contracts
Trading Derivatives
Trading account activities	$ 18	$ 11

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://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4F
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=109980867&loc=SL5624186-113959

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-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://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 940
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-URI http://asc.fasb.org/extlink&oid=35711157&loc=d3e42567-110969

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 220
-Section S99
-Paragraph 1
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-URI http://asc.fasb.org/extlink&oid=116637391&loc=SL114874048-224260

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