Allowance for Credit Losses - Rollforward of Allowance for Credit Losses (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	$ 963	$ 200	$ 180
Charge-offs	(59)	(156)	(59)
Recoveries	57	36	32
Initial allowance on loans purchased with credit deterioration		287
Provision for credit losses	(310)	503	45
Ending balance	670	963	$ 200	$ 180
Accounting Standards Update [Extensible List]			Accounting Standards Update 2016-13 [Member]	Accounting Standards Update 2016-02 [Member]
Loans and leases	54,859	58,232
Adjustment
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance		107
Ending balance			$ 107
Adjusted Balance
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance		307
Ending balance			307
Financial Asset Acquired with Credit Deterioration
Allowance for Loan and Lease Losses [Roll Forward]
Additions in allowance for credit loss		287
Funded and Unfunded Loan Commitments
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	1,048	206
Ending balance	736	1,048	206
Funded Commitments
Allowance for Loan and Lease Losses [Roll Forward]
Provision for credit losses	(291)	489	47
Unfunded Commitment
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	85	6	7
Provision for credit losses	(19)	14	(1)
Initial reserve on loans acquired		41
Ending balance	66	85	6	$ 7
Unfunded Commitment | Adjustment
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance		24
Ending balance			24
Unfunded Commitment | Adjusted Balance
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance		30
Ending balance			30
Commercial
Allowance for Loan and Lease Losses [Roll Forward]
Loans and leases	31,068	33,104
Commercial | C&I
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	453	123	99
Charge-offs	(34)	(129)	(34)
Recoveries	21	9	7
Initial allowance on loans purchased with credit deterioration		138
Ending balance	334	453	123	99
Loans and leases	31,068	33,104
Commercial | C&I | PCD Loans
Allowance for Loan and Lease Losses [Roll Forward]
Charge-offs		(237)
Commercial | C&I | Non-PCD Loans
Allowance for Loan and Lease Losses [Roll Forward]
Provision for credit losses		147
Commercial | C&I | Adjustment
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance		19
Ending balance			19
Commercial | C&I | Adjusted Balance
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance		142
Ending balance			142
Commercial | C&I | Paycheck Protection Plan
Allowance for Loan and Lease Losses [Roll Forward]
Loans and leases	1,000	4,100
Commercial | C&I | Funded and Unfunded Loan Commitments
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	518	127
Ending balance	380	518	127
Commercial | C&I | Funded Commitments
Allowance for Loan and Lease Losses [Roll Forward]
Provision for credit losses	(106)	293	51
Commercial | C&I | Unfunded Commitment
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	65	4	4
Provision for credit losses	(19)	32	0
Initial reserve on loans acquired		12
Ending balance	46	65	4	4
Commercial | C&I | Unfunded Commitment | Adjustment
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance		17
Ending balance			17
Commercial | C&I | Unfunded Commitment | Adjusted Balance
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance		21
Ending balance			21
Commercial | Commercial Real Estate
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	242	36	31
Charge-offs	(5)	(5)	(1)
Recoveries	5	4	1
Initial allowance on loans purchased with credit deterioration		100
Ending balance	154	242	36	31
Loans and leases	12,109	12,275
Commercial | Commercial Real Estate | Adjustment
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance		(7)
Ending balance			(7)
Commercial | Commercial Real Estate | Adjusted Balance
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance		29
Ending balance			29
Commercial | Commercial Real Estate | Funded and Unfunded Loan Commitments
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	252	38
Ending balance	166	252	38
Commercial | Commercial Real Estate | Funded Commitments
Allowance for Loan and Lease Losses [Roll Forward]
Provision for credit losses	(88)	114	5
Commercial | Commercial Real Estate | Unfunded Commitment
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	10	2	3
Provision for credit losses	2	(19)	(1)
Initial reserve on loans acquired		26
Ending balance	12	10	2	3
Commercial | Commercial Real Estate | Unfunded Commitment | Adjustment
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance		1
Ending balance			1
Commercial | Commercial Real Estate | Unfunded Commitment | Adjusted Balance
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance		3
Ending balance			3
Consumer
Allowance for Loan and Lease Losses [Roll Forward]
Loans and leases	10,772	11,725
Consumer | Consumer real estate
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	242	28	37
Charge-offs	(5)	(8)	(8)
Recoveries	27	18	20
Initial allowance on loans purchased with credit deterioration		44
Ending balance	163	242	28	37
Loans and leases	10,772	11,725
Consumer | Consumer real estate | Adjustment
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance		93
Ending balance			93
Consumer | Consumer real estate | Adjusted Balance
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance		121
Ending balance			121
Consumer | Consumer real estate | Funded and Unfunded Loan Commitments
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	252	28
Ending balance	171	252	28
Consumer | Consumer real estate | Funded Commitments
Allowance for Loan and Lease Losses [Roll Forward]
Provision for credit losses	(101)	67	(21)
Consumer | Consumer real estate | Unfunded Commitment
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	10	0	0
Provision for credit losses	(2)	1	0
Initial reserve on loans acquired		3
Ending balance	8	10	0	0
Consumer | Consumer real estate | Unfunded Commitment | Adjustment
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance		6
Ending balance			6
Consumer | Consumer real estate | Unfunded Commitment | Adjusted Balance
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance		6
Ending balance			6
Consumer | Credit card and other
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	26	13	13
Charge-offs	(15)	(14)	(16)
Recoveries	4	5	4
Initial allowance on loans purchased with credit deterioration		5
Ending balance	19	26	13	13
Loans and leases	910	1,128
Consumer | Credit card and other | Adjustment
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance		2
Ending balance			2
Consumer | Credit card and other | Adjusted Balance
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance		15
Ending balance			15
Consumer | Credit card and other | Funded and Unfunded Loan Commitments
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	26	13
Ending balance	19	26	13
Consumer | Credit card and other | Funded Commitments
Allowance for Loan and Lease Losses [Roll Forward]
Provision for credit losses	4	15	12
Consumer | Credit card and other | Unfunded Commitment
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	0	0	0
Provision for credit losses	0	0	0
Initial reserve on loans acquired		0
Ending balance	$ 0	0	0	$ 0
Consumer | Credit card and other | Unfunded Commitment | Adjustment
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance		0
Ending balance			0
Consumer | Credit card and other | Unfunded Commitment | Adjusted Balance
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance		$ 0
Ending balance			$ 0