Allowance for Credit Losses - Rollforward of Allowance for Credit Losses (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	$ 815	$ 538	$ 963	$ 307
Charge-offs	(19)	(78)	(48)	(115)
Recoveries	16	11	47	24
Provision for credit losses	(85)	227	(245)	502
Ending balance	734	988	734	988
Loans and leases	55,435		55,435		$ 58,232
Financial Asset Acquired with Credit Deterioration
Allowance for Loan and Lease Losses [Roll Forward]
Initial allowance on loans purchased with credit deterioration		287		287
Funded commitment
Allowance for Loan and Lease Losses [Roll Forward]
Provision for credit losses	(78)	230	(228)	485
Unfunded commitment
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	75	51	85	31
Initial reserve on loans acquired		41		41
Provision for credit losses	(7)	(3)	(17)	17
Ending balance	68	89	68	89
Commercial \| Commercial and industrial
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	385	319	453	142
Charge-offs	(11)	(69)	(27)	(95)
Recoveries	7	3	18	5
Ending balance	374	489	374	489
Loans and leases	31,516		31,516		33,104
Commercial \| Commercial and industrial \| Financial Asset Acquired with Credit Deterioration
Allowance for Loan and Lease Losses [Roll Forward]
Initial allowance on loans purchased with credit deterioration		138		138
Commercial \| Commercial and industrial \| Paycheck Protection Plan
Allowance for Loan and Lease Losses [Roll Forward]
Loans and leases	2,000		2,000		4,100
Commercial \| Commercial and industrial \| Funded commitment
Allowance for Loan and Lease Losses [Roll Forward]
Provision for credit losses	(7)	98	(70)	299
Commercial \| Commercial and industrial \| Unfunded commitment
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	57	37	65	21
Initial reserve on loans acquired		12		12
Provision for credit losses	(8)	(2)	(16)	14
Ending balance	49	47	49	47
Commercial \| Commercial Real Estate
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	210	57	242	29
Charge-offs	(2)	(4)	(5)	(4)
Recoveries	2	2	5	3
Ending balance	162	208	162	208
Loans and leases	12,194		12,194		12,275
Commercial \| Commercial Real Estate \| Financial Asset Acquired with Credit Deterioration
Allowance for Loan and Lease Losses [Roll Forward]
Initial allowance on loans purchased with credit deterioration		100		100
Commercial \| Commercial Real Estate \| Funded commitment
Allowance for Loan and Lease Losses [Roll Forward]
Provision for credit losses	(48)	53	(80)	80
Commercial \| Commercial Real Estate \| Unfunded commitment
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	9	6	10	4
Initial reserve on loans acquired		26		26
Provision for credit losses	1	(1)	0	1
Ending balance	10	31	10	31
Consumer
Allowance for Loan and Lease Losses [Roll Forward]
Loans and leases	10,787		10,787		11,725
Consumer \| Consumer Real Estate
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	203	144	242	121
Charge-offs	(1)	(2)	(5)	(6)
Recoveries	7	5	21	13
Ending balance	179	265	179	265
Loans and leases	10,787		10,787		11,725
Consumer \| Consumer Real Estate \| Financial Asset Acquired with Credit Deterioration
Allowance for Loan and Lease Losses [Roll Forward]
Initial allowance on loans purchased with credit deterioration		44		44
Consumer \| Consumer Real Estate \| Funded commitment
Allowance for Loan and Lease Losses [Roll Forward]
Provision for credit losses	(30)	74	(79)	93
Consumer \| Consumer Real Estate \| Unfunded commitment
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	9	8	10	6
Initial reserve on loans acquired		3		3
Provision for credit losses	0	0	(1)	2
Ending balance	9	11	9	11
Consumer \| Credit Card and Other
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	17	18	26	15
Charge-offs	(5)	(3)	(11)	(10)
Recoveries	0	1	3	3
Ending balance	19	26	19	26
Loans and leases	938		938		$ 1,128
Consumer \| Credit Card and Other \| Financial Asset Acquired with Credit Deterioration
Allowance for Loan and Lease Losses [Roll Forward]
Initial allowance on loans purchased with credit deterioration		5		5
Consumer \| Credit Card and Other \| Funded commitment
Allowance for Loan and Lease Losses [Roll Forward]
Provision for credit losses	7	5	1	13
Consumer \| Credit Card and Other \| Unfunded commitment
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	0	0	0	0
Initial reserve on loans acquired		0		0
Provision for credit losses	0	0	0	0
Ending balance	$ 0	$ 0	$ 0	$ 0

Financing Receivable, Credit Loss, Initial Reserve on Loans Acquired

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- Definition

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

+ References

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Amount excluding accrued interest, of allowance for credit loss on financing receivable.

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 45
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Amount of increase in allowance for credit loss on financing receivable purchased with credit deterioration.

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Amount of increase in allowance for credit loss on financing receivable from recovery.

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Amount of writeoff of financing receivable, charged against allowance for credit loss.

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Amount excluding accrued interest, before allowance for credit loss, of financing receivable.

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Amount of credit loss expense (reversal of expense) for financing receivable.

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