Derivatives and Hedging Activities - Cumulative Basis Adjustments on Fair Value Hedges (Details) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Derivatives, Fair Value [Line Items]
Securities available for sale	$ 45,364	$ 27,556
Long-term Debt \| Interest rate
Derivatives, Fair Value [Line Items]
Carrying amount of hedged item	7,553	8,182
Hedge accounting basis adjustment	138	416
Securities available for sale \| Interest rate
Derivatives, Fair Value [Line Items]
Carrying amount of hedged item	6,280	2,080
Hedge accounting basis adjustment	134	(21)
Securities available for sale	7,700	2,500
Not Designated as Hedging Instrument \| Long-term Debt \| Interest rate
Derivatives, Fair Value [Line Items]
Hedge accounting basis adjustment	$ (7)	$ (8)

Amount excluding accrued interest, of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 30
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=124258926&loc=SL82898722-210454

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+ References

No definition available.

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- Definition

Amount of cumulative increase (decrease) in fair value of hedged asset in fair value hedge, attributable to hedged risk.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4EE
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=125515794&loc=SL109999712-113959

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- Definition

Amount of liability hedged in fair value hedging relationship.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4EE
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=125515794&loc=SL109999712-113959

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