Loans and asset quality - Credit Risk Profile by Grade (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2021	Dec. 31, 2020
Financing Receivable, Credit Quality Indicator [Line Items]
Originated, at amortized cost, current fiscal year	$ 10,987	$ 7,414
Originated, at amortized cost, fiscal year before current fiscal year	2,591	2,976
Originated, at amortized cost, two years before current fiscal year	2,412	1,887
Originated, at amortized cost, three years before current fiscal year	1,097	2,591
Originated, at amortized cost, four years before current fiscal year	1,645	2,352
Originated, at amortized cost, more than five years before current fiscal year	5,051	4,506
Amortized cost	35,966	32,033
Converted to term loans – Amortized cost	26	27
Total	59,775	53,786
Accrued interest receivable	56	59
Loans	64,328	56,469
Wealth management mortgages
Financing Receivable, Credit Quality Indicator [Line Items]
Originated, at amortized cost, current fiscal year	1,468	1,117
Originated, at amortized cost, fiscal year before current fiscal year	1,036	1,044
Originated, at amortized cost, two years before current fiscal year	899	637
Originated, at amortized cost, three years before current fiscal year	561	1,188
Originated, at amortized cost, four years before current fiscal year	944	1,515
Originated, at amortized cost, more than five years before current fiscal year	3,084	2,546
Amortized cost	27	38
Converted to term loans – Amortized cost	0	0
Total	8,019	8,085
Wealth management loans and mortgages
Financing Receivable, Credit Quality Indicator [Line Items]
Originated, at amortized cost, current fiscal year	1,537	1,135
Originated, at amortized cost, fiscal year before current fiscal year	1,051	1,129
Originated, at amortized cost, two years before current fiscal year	973	648
Originated, at amortized cost, three years before current fiscal year	565	1,335
Originated, at amortized cost, four years before current fiscal year	1,097	1,574
Originated, at amortized cost, more than five years before current fiscal year	3,209	2,658
Amortized cost	9,555	7,878
Converted to term loans – Amortized cost	0	0
Total	17,987	16,357
Accrued interest receivable	28	27
Other residential mortgages
Financing Receivable, Credit Quality Indicator [Line Items]
Originated, at amortized cost, current fiscal year	0	0
Originated, at amortized cost, fiscal year before current fiscal year	0	0
Originated, at amortized cost, two years before current fiscal year	0	0
Originated, at amortized cost, three years before current fiscal year	0	0
Originated, at amortized cost, four years before current fiscal year	0	0
Originated, at amortized cost, more than five years before current fiscal year	317	389
Amortized cost	0	0
Converted to term loans – Amortized cost	0	0
Total	317	389
Accrued interest receivable	1	1
Other loans
Financing Receivable, Credit Quality Indicator [Line Items]
Originated, at amortized cost, current fiscal year	0	0
Originated, at amortized cost, fiscal year before current fiscal year	0	0
Originated, at amortized cost, two years before current fiscal year	0	0
Originated, at amortized cost, three years before current fiscal year	0	0
Originated, at amortized cost, four years before current fiscal year	0	0
Originated, at amortized cost, more than five years before current fiscal year	0	0
Amortized cost	2,362	1,904
Converted to term loans – Amortized cost	0	0
Total	2,362	1,904
Accrued interest receivable	1	1
Margin loans
Financing Receivable, Credit Quality Indicator [Line Items]
Originated, at amortized cost, current fiscal year	6,254	4,614
Originated, at amortized cost, fiscal year before current fiscal year	800	0
Originated, at amortized cost, two years before current fiscal year	0	0
Originated, at amortized cost, three years before current fiscal year	0	0
Originated, at amortized cost, four years before current fiscal year	0	0
Originated, at amortized cost, more than five years before current fiscal year	0	0
Amortized cost	13,767	10,802
Converted to term loans – Amortized cost	0	0
Total	20,821	15,416
Accrued interest receivable	8	8
Loans	20,800	15,400
Overdrafts
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	$ 4,600	2,700
Overdraft repayment period	2 days
Overdrafts | Overdrafts
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	$ 4,553	2,683
Investment grade | Loans receivable
Financing Receivable, Credit Quality Indicator [Line Items]
Originated, at amortized cost, current fiscal year	67	18
Originated, at amortized cost, fiscal year before current fiscal year	15	85
Originated, at amortized cost, two years before current fiscal year	74	11
Originated, at amortized cost, three years before current fiscal year	4	147
Originated, at amortized cost, four years before current fiscal year	153	59
Originated, at amortized cost, more than five years before current fiscal year	125	112
Amortized cost	9,500	7,786
Converted to term loans – Amortized cost	0	0
Total	9,938	8,218
Non-investment grade | Loans receivable
Financing Receivable, Credit Quality Indicator [Line Items]
Originated, at amortized cost, current fiscal year	2	0
Originated, at amortized cost, fiscal year before current fiscal year	0	0
Originated, at amortized cost, two years before current fiscal year	0	0
Originated, at amortized cost, three years before current fiscal year	0	0
Originated, at amortized cost, four years before current fiscal year	0	0
Originated, at amortized cost, more than five years before current fiscal year	0	0
Amortized cost	28	54
Converted to term loans – Amortized cost	0	0
Total	30	54
Commercial
Financing Receivable, Credit Quality Indicator [Line Items]
Originated, at amortized cost, current fiscal year	491	270
Originated, at amortized cost, fiscal year before current fiscal year	43	18
Originated, at amortized cost, two years before current fiscal year	0	77
Originated, at amortized cost, three years before current fiscal year	0	420
Originated, at amortized cost, four years before current fiscal year	195	57
Originated, at amortized cost, more than five years before current fiscal year	57	0
Amortized cost	889	587
Converted to term loans – Amortized cost	0	0
Total	1,675	1,429
Accrued interest receivable	0	2
Commercial | Investment grade
Financing Receivable, Credit Quality Indicator [Line Items]
Originated, at amortized cost, current fiscal year	401	128
Originated, at amortized cost, fiscal year before current fiscal year	20	18
Originated, at amortized cost, two years before current fiscal year	0	71
Originated, at amortized cost, three years before current fiscal year	0	420
Originated, at amortized cost, four years before current fiscal year	195	57
Originated, at amortized cost, more than five years before current fiscal year	57	0
Amortized cost	818	493
Converted to term loans – Amortized cost	0	0
Total	1,491	1,187
Commercial | Non-investment grade
Financing Receivable, Credit Quality Indicator [Line Items]
Originated, at amortized cost, current fiscal year	90	142
Originated, at amortized cost, fiscal year before current fiscal year	23	0
Originated, at amortized cost, two years before current fiscal year	0	6
Originated, at amortized cost, three years before current fiscal year	0	0
Originated, at amortized cost, four years before current fiscal year	0	0
Originated, at amortized cost, more than five years before current fiscal year	0	0
Amortized cost	71	94
Converted to term loans – Amortized cost	0	0
Total	184	242
Commercial real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Originated, at amortized cost, current fiscal year	1,878	1,063
Originated, at amortized cost, fiscal year before current fiscal year	616	1,629
Originated, at amortized cost, two years before current fiscal year	1,418	1,101
Originated, at amortized cost, three years before current fiscal year	521	702
Originated, at amortized cost, four years before current fiscal year	349	688
Originated, at amortized cost, more than five years before current fiscal year	757	490
Amortized cost	827	356
Converted to term loans – Amortized cost	26	27
Total	6,392	6,056
Accrued interest receivable	8	8
Commercial real estate | Investment grade
Financing Receivable, Credit Quality Indicator [Line Items]
Originated, at amortized cost, current fiscal year	1,265	778
Originated, at amortized cost, fiscal year before current fiscal year	524	1,010
Originated, at amortized cost, two years before current fiscal year	793	458
Originated, at amortized cost, three years before current fiscal year	166	543
Originated, at amortized cost, four years before current fiscal year	275	312
Originated, at amortized cost, more than five years before current fiscal year	651	346
Amortized cost	670	127
Converted to term loans – Amortized cost	0	0
Total	4,344	3,574
Commercial real estate | Non-investment grade
Financing Receivable, Credit Quality Indicator [Line Items]
Originated, at amortized cost, current fiscal year	613	285
Originated, at amortized cost, fiscal year before current fiscal year	92	619
Originated, at amortized cost, two years before current fiscal year	625	643
Originated, at amortized cost, three years before current fiscal year	355	159
Originated, at amortized cost, four years before current fiscal year	74	376
Originated, at amortized cost, more than five years before current fiscal year	106	144
Amortized cost	157	229
Converted to term loans – Amortized cost	26	27
Total	2,048	2,482
Financial institutions
Financing Receivable, Credit Quality Indicator [Line Items]
Originated, at amortized cost, current fiscal year	804	216
Originated, at amortized cost, fiscal year before current fiscal year	0	182
Originated, at amortized cost, two years before current fiscal year	6	47
Originated, at amortized cost, three years before current fiscal year	0	125
Originated, at amortized cost, four years before current fiscal year	0	13
Originated, at amortized cost, more than five years before current fiscal year	72	156
Amortized cost	8,566	10,506
Converted to term loans – Amortized cost	0	0
Total	9,448	11,245
Accrued interest receivable	10	12
Financial institutions | Investment grade
Financing Receivable, Credit Quality Indicator [Line Items]
Originated, at amortized cost, current fiscal year	759	132
Originated, at amortized cost, fiscal year before current fiscal year	0	146
Originated, at amortized cost, two years before current fiscal year	0	47
Originated, at amortized cost, three years before current fiscal year	0	125
Originated, at amortized cost, four years before current fiscal year	0	13
Originated, at amortized cost, more than five years before current fiscal year	72	156
Amortized cost	6,949	8,760
Converted to term loans – Amortized cost	0	0
Total	7,780	9,379
Financial institutions | Non-investment grade
Financing Receivable, Credit Quality Indicator [Line Items]
Originated, at amortized cost, current fiscal year	45	84
Originated, at amortized cost, fiscal year before current fiscal year	0	36
Originated, at amortized cost, two years before current fiscal year	6	0
Originated, at amortized cost, three years before current fiscal year	0	0
Originated, at amortized cost, four years before current fiscal year	0	0
Originated, at amortized cost, more than five years before current fiscal year	0	0
Amortized cost	1,617	1,746
Converted to term loans – Amortized cost	0	0
Total	1,668	1,866
Lease financings
Financing Receivable, Credit Quality Indicator [Line Items]
Originated, at amortized cost, current fiscal year	23	116
Originated, at amortized cost, fiscal year before current fiscal year	81	18
Originated, at amortized cost, two years before current fiscal year	15	14
Originated, at amortized cost, three years before current fiscal year	11	9
Originated, at amortized cost, four years before current fiscal year	4	20
Originated, at amortized cost, more than five years before current fiscal year	639	813
Amortized cost	0	0
Converted to term loans – Amortized cost	0	0
Total	773	990
Accrued interest receivable	$ 0	$ 0