Loans and Related Allowance for Credit Losses (Rollforward of Allowance for Credit Losses of Loans and Leases) (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2023
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	$ 4,791	$ 4,741	$ 4,741
Charge-offs	(330)	(282)
Recoveries	87	87
Net (charge-offs)	(243)	(195)
Provision for credit losses	147	229
Other	(2)	1
Ending balance	4,693	4,741	4,791
Off-Balance Sheet, Credit Loss, Liability [Roll Forward]
Beginning balance	663	694	694
Provision for (recapture of) credit losses	9	(22)
Ending balance	672	672	663
Allowance for credit loss	5,365	5,413	5,500
Allowances for investment securities and other financial assets	117	205
Cumulative Effect, Period of Adoption, Adjustment
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance		(35)	(35)
Cumulative Effect, Period of Adoption, Adjusted Balance
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	4,791	4,706	4,706
Ending balance			4,791
Total commercial
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	3,259	3,114	3,114
Charge-offs	(148)	(120)	(442)
Recoveries	23	25
Net (charge-offs)	(125)	(95)
Provision for credit losses	85	25
Other	(2)	2
Ending balance	3,217	3,046	3,259
Off-Balance Sheet, Credit Loss, Liability [Roll Forward]
Beginning balance	545	613	613
Provision for (recapture of) credit losses	(17)	(53)
Ending balance	528	560	545
Allowance for credit loss	3,745	3,606
Total commercial | Cumulative Effect, Period of Adoption, Adjusted Balance
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	3,259	3,114	3,114
Ending balance			3,259
Total consumer
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	1,532	1,627	1,627
Charge-offs	(182)	(162)
Recoveries	64	62
Net (charge-offs)	(118)	(100)
Provision for credit losses	62	204
Other		(1)
Ending balance	1,476	1,695	1,532
Off-Balance Sheet, Credit Loss, Liability [Roll Forward]
Beginning balance	118	81	81
Provision for (recapture of) credit losses	26	31
Ending balance	144	112	118
Allowance for credit loss	1,620	1,807
Total consumer | Cumulative Effect, Period of Adoption, Adjustment
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance		(35)	(35)
Total consumer | Cumulative Effect, Period of Adoption, Adjusted Balance
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	$ 1,532	$ 1,592	1,592
Ending balance			$ 1,532