Loans - Commercial Banking: Risk Profile by Internal Risk Rating (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020	Mar. 31, 2020
Financing Receivable, Allowance for Credit Loss [Line Items]
Total Loans	$ 243,131	$ 251,624	$ 262,990
Commercial Banking
Financing Receivable, Allowance for Credit Loss [Line Items]
Term Loans by Vintage Year One	2,892	14,262
Term Loans by Vintage Year Two	12,977	14,181
Term Loans by Vintage Year Three	13,513	8,366
Term Loans by Vintage Year Four	7,974	4,818
Term Loans by Vintage Year Five	4,394	3,990
Term Loans by Vintage After Year Five	12,627	9,561
Total Term Loans	54,377	55,178
Revolving Loans	19,297	20,455
Revolving Loans Converted to Term	128	147
Total Loans	73,802	75,780
Loans under Paycheck Protection Program	275	238
Commercial Banking \| Commercial and multifamily real estate
Financing Receivable, Allowance for Credit Loss [Line Items]
Term Loans by Vintage Year One	764	4,111
Term Loans by Vintage Year Two	3,802	5,389
Term Loans by Vintage Year Three	5,306	3,777
Term Loans by Vintage Year Four	3,718	1,798
Term Loans by Vintage Year Five	1,587	2,043
Term Loans by Vintage After Year Five	7,913	6,312
Total Term Loans	23,090	23,430
Revolving Loans	6,893	7,226
Revolving Loans Converted to Term	25	25
Total Loans	30,008	30,681
Commercial Banking \| Commercial and multifamily real estate \| Noncriticized
Financing Receivable, Allowance for Credit Loss [Line Items]
Term Loans by Vintage Year One	610	3,791
Term Loans by Vintage Year Two	3,498	4,932
Term Loans by Vintage Year Three	4,788	3,232
Term Loans by Vintage Year Four	3,200	1,437
Term Loans by Vintage Year Five	1,230	1,649
Term Loans by Vintage After Year Five	5,997	4,904
Total Term Loans	19,323	19,945
Revolving Loans	6,845	7,114
Revolving Loans Converted to Term	0	0
Total Loans	26,168	27,059
Commercial Banking \| Commercial and multifamily real estate \| Criticized \| Criticized performing
Financing Receivable, Allowance for Credit Loss [Line Items]
Term Loans by Vintage Year One	154	320
Term Loans by Vintage Year Two	304	446
Term Loans by Vintage Year Three	507	515
Term Loans by Vintage Year Four	488	355
Term Loans by Vintage Year Five	351	391
Term Loans by Vintage After Year Five	1,729	1,258
Total Term Loans	3,533	3,285
Revolving Loans	48	112
Revolving Loans Converted to Term	25	25
Total Loans	3,606	3,422
Commercial Banking \| Commercial and multifamily real estate \| Criticized \| Criticized nonperforming
Financing Receivable, Allowance for Credit Loss [Line Items]
Term Loans by Vintage Year One	0	0
Term Loans by Vintage Year Two	0	11
Term Loans by Vintage Year Three	11	30
Term Loans by Vintage Year Four	30	6
Term Loans by Vintage Year Five	6	3
Term Loans by Vintage After Year Five	187	150
Total Term Loans	234	200
Revolving Loans	0	0
Revolving Loans Converted to Term	0	0
Total Loans	234	200
Commercial Banking \| Commercial and industrial
Financing Receivable, Allowance for Credit Loss [Line Items]
Term Loans by Vintage Year One	2,128	10,151
Term Loans by Vintage Year Two	9,175	8,792
Term Loans by Vintage Year Three	8,207	4,589
Term Loans by Vintage Year Four	4,256	3,020
Term Loans by Vintage Year Five	2,807	1,947
Term Loans by Vintage After Year Five	4,714	3,249
Total Term Loans	31,287	31,748
Revolving Loans	12,404	13,229
Revolving Loans Converted to Term	103	122
Total Loans	43,794	45,099
Commercial Banking \| Commercial and industrial \| Noncriticized
Financing Receivable, Allowance for Credit Loss [Line Items]
Term Loans by Vintage Year One	2,024	9,761
Term Loans by Vintage Year Two	8,846	7,890
Term Loans by Vintage Year Three	7,223	4,043
Term Loans by Vintage Year Four	3,851	2,717
Term Loans by Vintage Year Five	2,552	1,832
Term Loans by Vintage After Year Five	4,483	3,034
Total Term Loans	28,979	29,277
Revolving Loans	11,091	11,548
Revolving Loans Converted to Term	61	80
Total Loans	40,131	40,905
Commercial Banking \| Commercial and industrial \| Criticized \| Criticized performing
Financing Receivable, Allowance for Credit Loss [Line Items]
Term Loans by Vintage Year One	85	316
Term Loans by Vintage Year Two	255	794
Term Loans by Vintage Year Three	926	521
Term Loans by Vintage Year Four	330	252
Term Loans by Vintage Year Five	202	106
Term Loans by Vintage After Year Five	226	215
Total Term Loans	2,024	2,204
Revolving Loans	1,149	1,498
Revolving Loans Converted to Term	42	42
Total Loans	3,215	3,744
Commercial Banking \| Commercial and industrial \| Criticized \| Criticized nonperforming
Financing Receivable, Allowance for Credit Loss [Line Items]
Term Loans by Vintage Year One	19	74
Term Loans by Vintage Year Two	74	108
Term Loans by Vintage Year Three	58	25
Term Loans by Vintage Year Four	75	51
Term Loans by Vintage Year Five	53	9
Term Loans by Vintage After Year Five	5	0
Total Term Loans	284	267
Revolving Loans	164	183
Revolving Loans Converted to Term	0	0
Total Loans	$ 448	$ 450

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