Loans and asset quality - Credit Risk Profile by Origination (Details) $ in Millions	Sep. 30, 2020 USD ($)
Financing Receivable, Credit Quality Indicator [Line Items]
YTD20	$ 5,658
2019	3,180
2018	2,006
2017	2,703
2016	2,526
Prior to 2016	4,884
Amortized cost	30,542
Converted to term loans - Amortized cost	29
Total	51,528
Accrued interest receivable	61
Wealth management mortgages
Financing Receivable, Credit Quality Indicator [Line Items]
YTD20	781
2019	1,082
2018	682
2017	1,267
2016	1,622
Prior to 2016	2,748
Amortized cost	34
Converted to term loans - Amortized cost	0
Total	8,216
Wealth management loans and mortgages
Financing Receivable, Credit Quality Indicator [Line Items]
YTD20	812
2019	1,162
2018	693
2017	1,416
2016	1,678
Prior to 2016	2,833
Amortized cost	7,332
Converted to term loans - Amortized cost	0
Total	15,926
Accrued interest receivable	29
Other residential mortgages
Financing Receivable, Credit Quality Indicator [Line Items]
YTD20	0
2019	0
2018	0
2017	0
2016	0
Prior to 2016	423
Amortized cost	0
Converted to term loans - Amortized cost	0
Total	423
Accrued interest receivable	2
Other loans
Financing Receivable, Credit Quality Indicator [Line Items]
YTD20	0
2019	0
2018	0
2017	0
2016	0
Prior to 2016	0
Amortized cost	1,658
Converted to term loans - Amortized cost	0
Total	1,658
Accrued interest receivable	1
Margin loans
Financing Receivable, Credit Quality Indicator [Line Items]
YTD20	3,553
2019	0
2018	0
2017	0
2016	0
Prior to 2016	0
Amortized cost	9,945
Converted to term loans - Amortized cost	0
Total	13,498
Accrued interest receivable	7
Investment grade | Loans receivable
Financing Receivable, Credit Quality Indicator [Line Items]
YTD20	31
2019	80
2018	11
2017	149
2016	56
Prior to 2016	85
Amortized cost	7,235
Converted to term loans - Amortized cost	0
Total	7,647
Non-investment grade | Loans receivable
Financing Receivable, Credit Quality Indicator [Line Items]
YTD20	0
2019	0
2018	0
2017	0
2016	0
Prior to 2016	0
Amortized cost	63
Converted to term loans - Amortized cost	0
Total	63
Commercial
Financing Receivable, Credit Quality Indicator [Line Items]
YTD20	238
2019	134
2018	103
2017	450
2016	57
Prior to 2016	0
Amortized cost	959
Converted to term loans - Amortized cost	0
Total	1,941
Accrued interest receivable	1
Commercial | Investment grade
Financing Receivable, Credit Quality Indicator [Line Items]
YTD20	153
2019	73
2018	96
2017	450
2016	57
Prior to 2016	0
Amortized cost	893
Converted to term loans - Amortized cost	0
Total	1,722
Commercial | Non-investment grade
Financing Receivable, Credit Quality Indicator [Line Items]
YTD20	85
2019	61
2018	7
2017	0
2016	0
Prior to 2016	0
Amortized cost	66
Converted to term loans - Amortized cost	0
Total	219
Commercial real estate
Financing Receivable, Credit Quality Indicator [Line Items]
YTD20	771
2019	1,591
2018	1,146
2017	702
2016	752
Prior to 2016	582
Amortized cost	419
Converted to term loans - Amortized cost	29
Total	5,992
Accrued interest receivable	8
Commercial real estate | Investment grade
Financing Receivable, Credit Quality Indicator [Line Items]
YTD20	611
2019	1,065
2018	542
2017	543
2016	385
Prior to 2016	430
Amortized cost	175
Converted to term loans - Amortized cost	0
Total	3,751
Commercial real estate | Non-investment grade
Financing Receivable, Credit Quality Indicator [Line Items]
YTD20	160
2019	526
2018	604
2017	159
2016	367
Prior to 2016	152
Amortized cost	244
Converted to term loans - Amortized cost	29
Total	2,241
Financial institutions
Financing Receivable, Credit Quality Indicator [Line Items]
YTD20	158
2019	274
2018	47
2017	125
2016	14
Prior to 2016	165
Amortized cost	10,229
Converted to term loans - Amortized cost	0
Total	11,012
Accrued interest receivable	13
Financial institutions | Investment grade
Financing Receivable, Credit Quality Indicator [Line Items]
YTD20	60
2019	238
2018	47
2017	125
2016	14
Prior to 2016	165
Amortized cost	8,471
Converted to term loans - Amortized cost	0
Total	9,120
Financial institutions | Non-investment grade
Financing Receivable, Credit Quality Indicator [Line Items]
YTD20	98
2019	36
2018	0
2017	0
2016	0
Prior to 2016	0
Amortized cost	1,758
Converted to term loans - Amortized cost	0
Total	1,892
Lease financings
Financing Receivable, Credit Quality Indicator [Line Items]
YTD20	126
2019	19
2018	17
2017	10
2016	25
Prior to 2016	881
Amortized cost	0
Converted to term loans - Amortized cost	0
Total	1,078
Accrued interest receivable	$ 0