Loans and Related Allowance for Credit Losses (Rollforward of Allowance for Credit Losses of Loans and Leases) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020	Dec. 31, 2019
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	$ 5,361	$ 2,742
Charge-offs	(243)	(304)
Recoveries	97	92
Net (charge-offs)	(146)	(212)
Provision for (recapture of) credit losses	(502)	952
Other	1	(1)
Ending balance	4,714	3,944
Off-Balance Sheet, Credit Loss, Liability [Roll Forward]
Beginning balance	584	318
Provision for (recapture of) credit losses	(77)	(47)
Ending balance	507	450
Allowance for credit loss	5,221	4,394	$ 5,945	$ 3,060
Allowances for investment securities and other financial assets	136	21
Total commercial
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	3,337	1,812
Charge-offs	(69)	(83)
Recoveries	18	24
Net (charge-offs)	(51)	(59)
Provision for (recapture of) credit losses	(204)	531
Other	1	(1)
Ending balance	3,083	1,979
Off-Balance Sheet, Credit Loss, Liability [Roll Forward]
Beginning balance	485	316
Provision for (recapture of) credit losses	(82)	(25)
Ending balance	403	344
Allowance for credit loss	3,486	2,323	3,822	2,128
Total consumer
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	2,024	930
Charge-offs	(174)	(221)
Recoveries	79	68
Net (charge-offs)	(95)	(153)
Provision for (recapture of) credit losses	(298)	421
Ending balance	1,631	1,965
Off-Balance Sheet, Credit Loss, Liability [Roll Forward]
Beginning balance	99	2
Provision for (recapture of) credit losses	5	(22)
Ending balance	104	106
Allowance for credit loss	1,735	2,071	$ 2,123	$ 932
Cumulative Effect, Period of Adoption, Adjustment
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance		463
Off-Balance Sheet, Credit Loss, Liability [Roll Forward]
Beginning balance		179
Cumulative Effect, Period of Adoption, Adjustment | Total commercial
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance		(304)
Off-Balance Sheet, Credit Loss, Liability [Roll Forward]
Beginning balance		53
Cumulative Effect, Period of Adoption, Adjustment | Total consumer
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance		767
Off-Balance Sheet, Credit Loss, Liability [Roll Forward]
Beginning balance		126
Cumulative Effect, Period of Adoption, Adjusted Balance
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	5,361	3,205
Off-Balance Sheet, Credit Loss, Liability [Roll Forward]
Beginning balance	584	497
Cumulative Effect, Period of Adoption, Adjusted Balance | Total commercial
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	3,337	1,508
Off-Balance Sheet, Credit Loss, Liability [Roll Forward]
Beginning balance	485	369
Cumulative Effect, Period of Adoption, Adjusted Balance | Total consumer
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	2,024	1,697
Off-Balance Sheet, Credit Loss, Liability [Roll Forward]
Beginning balance	$ 99	$ 128