Allowance for Credit Losses - Rollforward of Allowance for Credit Losses (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	$ 914	$ 445	$ 963	$ 307
Charge-offs	(6)	(23)	(29)	(36)
Recoveries	16	6	31	12
Provision for credit losses	(115)	121	(160)	275
Ending balance	815	538	815	538
Loans and leases	56,687		56,687		$ 58,232
Funded commitment
Allowance for Loan and Lease Losses [Roll Forward]
Provision for credit losses	(109)	110	(150)	255
Unfunded commitment
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	81	39	85	30
Provision for credit losses	(6)	11	(10)	20
Ending balance	75	50	75	50
Commercial | Commercial and industrial
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	442	255	453	142
Charge-offs	(2)	(18)	(16)	(25)
Recoveries	5	1	11	2
Ending balance	385	319	385	319
Loans and leases	32,528		32,528		33,104
Commercial | Commercial and industrial | Paycheck Protection Plan
Allowance for Loan and Lease Losses [Roll Forward]
Loans and leases	3,800		3,800		4,100
Commercial | Commercial and industrial | Funded commitment
Allowance for Loan and Lease Losses [Roll Forward]
Provision for credit losses	(60)	81	(63)	200
Commercial | Commercial and industrial | Unfunded commitment
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	62	27	65	21
Provision for credit losses	(5)	9	(8)	15
Ending balance	57	36	57	36
Commercial | Commercial Real Estate
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	232	48	242	29
Charge-offs	0	0	(3)	(1)
Recoveries	1	0	3	1
Ending balance	210	57	210	57
Loans and leases	12,292		12,292		12,275
Commercial | Commercial Real Estate | Funded commitment
Allowance for Loan and Lease Losses [Roll Forward]
Provision for credit losses	(23)	9	(32)	28
Commercial | Commercial Real Estate | Unfunded commitment
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	11	6	10	3
Provision for credit losses	(2)	0	(1)	3
Ending balance	9	6	9	6
Consumer
Allowance for Loan and Lease Losses [Roll Forward]
Loans and leases	10,865		10,865		11,725
Consumer | Consumer Real Estate
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	222	123	242	121
Charge-offs	(1)	(2)	(4)	(4)
Recoveries	8	4	14	7
Ending balance	203	144	203	144
Loans and leases	10,865		10,865		11,725
Consumer | Consumer Real Estate | Funded commitment
Allowance for Loan and Lease Losses [Roll Forward]
Provision for credit losses	(26)	19	(49)	20
Consumer | Consumer Real Estate | Unfunded commitment
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	8	6	10	6
Provision for credit losses	1	2	(1)	2
Ending balance	9	8	9	8
Consumer | Credit Card and Other
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	18	19	26	15
Charge-offs	(3)	(3)	(6)	(6)
Recoveries	2	1	3	2
Ending balance	17	18	17	18
Loans and leases	1,002		1,002		$ 1,128
Consumer | Credit Card and Other | Funded commitment
Allowance for Loan and Lease Losses [Roll Forward]
Provision for credit losses	0	1	(6)	7
Consumer | Credit Card and Other | Unfunded commitment
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	0	0	0	0
Provision for credit losses	0	0	0	0
Ending balance	$ 0	$ 0	$ 0	$ 0