Investment Securities - Gains and Losses Recognized in Income from Securities (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Available-for-sale debt and other securities:
Realized gains	$ 0	$ 34	$ 1	$ 47
Realized losses	0	(33)	(1)	(47)
OTTI	0	(1)	0	(1)
Net realized losses on available-for sale debt and other securities	0	0	0	(1)
Total trading debt securities gains	0	2	3	5
Total equity securities (losses) gains	21	8	(3)	26
Total gains recognized in income from available-for-sale debt and other securities, trading debt securities and equity securities	21	10	0	30
Equity securities, unrealized gains (losses)	21	4	2	23
Commercial Banking Revenue and Wealth and Asset Management Revenue
Investment Holdings [Line Items]
Securities gains (losses)	$ 8	$ 1	$ 6	$ 4

Total available for sale and trading securities gains losses.

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Total trading securities gains losses.

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Amount of realized gain on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 9
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=121645371&loc=d3e27357-111563

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Amount of realized gain (loss) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 9
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=121645371&loc=d3e27357-111563

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Amount of realized loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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

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Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 321
-SubTopic 10
-Section 50
-Paragraph 4
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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).

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Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
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Amount of unrealized and realized gain (loss) on investment in marketable security, including other-than-temporary impairment (OTTI).

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Amount of other-than-temporary impairment (OTTI) on investment in debt security, recognized in earnings.

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-Publisher FASB
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-SubTopic 10
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