Loans and asset quality - Credit Risk Profile by Origination (Details) $ in Millions	Mar. 31, 2020 USD ($)
Financing Receivable, Credit Quality Indicator [Line Items]
1Q20	$ 3,030
2019	4,727
2018	2,299
2017	3,143
2016	2,951
Prior to 2016	5,586
Amortized cost	34,456
Converted to term loans - Amortized cost	29
Total	56,221
Accrued interest receivable	94
Wealth management mortgages
Financing Receivable, Credit Quality Indicator [Line Items]
1Q20	208
2019	1,139
2018	752
2017	1,438
2016	1,833
Prior to 2016	3,239
Amortized cost	41
Converted to term loans - Amortized cost	0
Total	8,650
Wealth management loans and mortgages
Financing Receivable, Credit Quality Indicator [Line Items]
1Q20	211
2019	1,222
2018	764
2017	1,616
2016	1,891
Prior to 2016	3,333
Amortized cost	7,222
Converted to term loans - Amortized cost	0
Total	16,259
Accrued interest receivable	38
Other residential mortgages
Financing Receivable, Credit Quality Indicator [Line Items]
1Q20	0
2019	0
2018	0
2017	0
2016	0
Prior to 2016	472
Amortized cost	0
Converted to term loans - Amortized cost	0
Total	472
Accrued interest receivable	2
Other loans
Financing Receivable, Credit Quality Indicator [Line Items]
1Q20	5
2019	0
2018	0
2017	0
2016	0
Prior to 2016	0
Amortized cost	1,214
Converted to term loans - Amortized cost	0
Total	1,219
Accrued interest receivable	1
Margin loans
Financing Receivable, Credit Quality Indicator [Line Items]
1Q20	2,260
2019	1,300
2018	0
2017	0
2016	0
Prior to 2016	0
Amortized cost	9,555
Converted to term loans - Amortized cost	0
Total	13,115
Accrued interest receivable	12
Investment grade | Loans receivable
Financing Receivable, Credit Quality Indicator [Line Items]
1Q20	3
2019	83
2018	12
2017	178
2016	58
Prior to 2016	94
Amortized cost	7,049
Converted to term loans - Amortized cost	0
Total	7,477
Non-investment grade | Loans receivable
Financing Receivable, Credit Quality Indicator [Line Items]
1Q20	0
2019	0
2018	0
2017	0
2016	0
Prior to 2016	0
Amortized cost	132
Converted to term loans - Amortized cost	0
Total	132
Commercial
Financing Receivable, Credit Quality Indicator [Line Items]
1Q20	61
2019	358
2018	119
2017	600
2016	63
Prior to 2016	0
Amortized cost	2,234
Converted to term loans - Amortized cost	0
Total	3,435
Accrued interest receivable	4
Commercial | Investment grade
Financing Receivable, Credit Quality Indicator [Line Items]
1Q20	20
2019	286
2018	107
2017	600
2016	57
Prior to 2016	0
Amortized cost	1,994
Converted to term loans - Amortized cost	0
Total	3,064
Commercial | Non-investment grade
Financing Receivable, Credit Quality Indicator [Line Items]
1Q20	41
2019	72
2018	12
2017	0
2016	6
Prior to 2016	0
Amortized cost	240
Converted to term loans - Amortized cost	0
Total	371
Commercial real estate
Financing Receivable, Credit Quality Indicator [Line Items]
1Q20	429
2019	1,548
2018	1,260
2017	730
2016	949
Prior to 2016	688
Amortized cost	818
Converted to term loans - Amortized cost	29
Total	6,451
Accrued interest receivable	11
Commercial real estate | Investment grade
Financing Receivable, Credit Quality Indicator [Line Items]
1Q20	414
2019	1,412
2018	1,047
2017	624
2016	636
Prior to 2016	640
Amortized cost	586
Converted to term loans - Amortized cost	0
Total	5,359
Commercial real estate | Non-investment grade
Financing Receivable, Credit Quality Indicator [Line Items]
1Q20	15
2019	136
2018	213
2017	106
2016	313
Prior to 2016	48
Amortized cost	232
Converted to term loans - Amortized cost	29
Total	1,092
Financial institutions
Financing Receivable, Credit Quality Indicator [Line Items]
1Q20	64
2019	278
2018	133
2017	125
2016	14
Prior to 2016	189
Amortized cost	13,413
Converted to term loans - Amortized cost	0
Total	14,216
Accrued interest receivable	26
Financial institutions | Investment grade
Financing Receivable, Credit Quality Indicator [Line Items]
1Q20	49
2019	270
2018	133
2017	125
2016	14
Prior to 2016	189
Amortized cost	11,429
Converted to term loans - Amortized cost	0
Total	12,209
Financial institutions | Non-investment grade
Financing Receivable, Credit Quality Indicator [Line Items]
1Q20	15
2019	8
2018	0
2017	0
2016	0
Prior to 2016	0
Amortized cost	1,984
Converted to term loans - Amortized cost	0
Total	2,007
Lease financings
Financing Receivable, Credit Quality Indicator [Line Items]
1Q20	0
2019	21
2018	23
2017	72
2016	34
Prior to 2016	904
Amortized cost	0
Converted to term loans - Amortized cost	0
Total	1,054
Accrued interest receivable	$ 0