Fair values of financial instruments carried at fair value - Quantitative information about significant unobservable inputs in Level 3 valuations (Details) - Recurring fair value measurement $ in Millions	Jun. 30, 2021 USD ($)	Dec. 31, 2020 USD ($)
Level 3
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Financial assets	$ 21,417	$ 20,300
Financial liabilities	11,515	9,656
Level 3 | Private equity including strategic investments
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Financial liabilities	206
Level 3 | Structured notes
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Financial liabilities	7,237	5,330
Level 3 | – equity-linked notes
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Financial liabilities	6,067
Level 3 | – FX-linked notes
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Financial liabilities	634
Level 3 | – other
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Financial liabilities	536
Level 3 | Other derivatives
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Financial liabilities	3,421	4,187
Level 3 | Other portfolios
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Financial liabilities	651	135
Level 3 | – other
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Financial liabilities	51
Level 3 | Private equity including strategic investments
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Financial assets	13,129	11,905
Level 3 | Asset-backed securities
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Financial assets	1,167	1,834
Level 3 | – CLO/CDO
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Financial assets	80
Level 3 | – other ABSs
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Financial assets	1,087
Level 3 | Derivatives with monolines
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Financial assets	52	$ 68
Level 3 | Other derivatives
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Financial assets	2,625
Level 3 | long-dated single stock options
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Financial assets	4,444
Level 3 | – repurchase agreements
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Financial assets	707
Financial liabilities	600
Level 3 | – other
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Financial assets	3,737
Level 3 | Interest rate
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Financial assets	1,199
Financial liabilities	999
Level 3 | Interest rate | securitisation swaps
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Financial liabilities	462
Level 3 | Interest rate | long-dated swaptions
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Financial liabilities	312
Level 3 | Interest rate | other
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Financial liabilities	225
Level 3 | Interest rate | securitisation swaps
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Financial assets	335
Level 3 | Interest rate | long-dated swaptions
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Financial assets	436
Level 3 | Interest rate | other
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Financial assets	428
Level 3 | Foreign exchange
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Financial assets	471
Financial liabilities	499
Level 3 | Foreign exchange | other
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Financial liabilities	184
Level 3 | Foreign exchange | FX options
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Financial liabilities	315
Level 3 | Foreign exchange | other
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Financial assets	213
Level 3 | Foreign exchange | FX options
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Financial assets	258
Level 3 | Equities
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Financial assets	885
Financial liabilities	1,813
Level 3 | Equities | other
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Financial liabilities	1,150
Level 3 | Equities | long-dated single stock options
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Financial liabilities	663
Level 3 | Equities | other
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Financial assets	420
Level 3 | Equities | long-dated single stock options
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Financial assets	465
Level 3 | Credit
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Financial assets	70
Financial liabilities	110
Level 3 | Credit | other
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Financial liabilities	110
Level 3 | Credit | other
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Financial assets	$ 70
Prepayment rate | Minimum | Interest rate | securitisation swaps
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Significant unobservable input, liabilities, percentage		0.06
Prepayment rate | Maximum | Interest rate | securitisation swaps
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Significant unobservable input, liabilities, percentage		0.06
Prepayment rate | Market proxy | Minimum | – CLO/CDO
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Significant unobservable input, assets, percentage	0	0
Prepayment rate | Market proxy | Maximum | – CLO/CDO
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Significant unobservable input, assets, percentage	0	0.09
Prepayment rate | Model – Discounted cash flow | Minimum | Interest rate | securitisation swaps
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Significant unobservable input, assets, percentage	0.05	0.06
Prepayment rate | Model – Discounted cash flow | Maximum | Interest rate | securitisation swaps
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Significant unobservable input, assets, percentage	0.10	0.06
Bid quotes | Market proxy | Minimum | – CLO/CDO
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Significant unobservable input, assets, percentage	0	0
Bid quotes | Market proxy | Minimum | – other ABSs
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Significant unobservable input, assets, percentage	0	0
Bid quotes | Market proxy | Maximum | – CLO/CDO
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Significant unobservable input, assets, percentage	100	100
Bid quotes | Market proxy | Maximum | – other ABSs
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Significant unobservable input, assets, percentage	172	101
Equity volatility | Minimum | Equities | long-dated single stock options
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Significant unobservable input, liabilities, percentage		0
Equity volatility | Maximum | Equities | long-dated single stock options
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Significant unobservable input, liabilities, percentage		1.20
Equity volatility | Model – Option model | Minimum | – equity-linked notes
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Significant unobservable input, liabilities, percentage	0.05	0.06
Equity volatility | Model – Option model | Minimum | Equities | long-dated single stock options
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Significant unobservable input, assets, percentage	0.02	0
Equity volatility | Model – Option model | Maximum | – equity-linked notes
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Significant unobservable input, liabilities, percentage	1.24	1.15
Equity volatility | Model – Option model | Maximum | Equities | long-dated single stock options
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Significant unobservable input, assets, percentage	1	1.20
Equity correlation | Model – Option model | Minimum | – equity-linked notes two
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Significant unobservable input, liabilities, percentage	0.07	(0.04)
Equity correlation | Model – Option model | Maximum | – equity-linked notes two
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Significant unobservable input, liabilities, percentage	0.98	0.88
FX volatility | Minimum | Foreign exchange | FX options
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Significant unobservable input, liabilities, percentage		0
FX volatility | Maximum | Foreign exchange | FX options
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Significant unobservable input, liabilities, percentage		0.43
FX volatility | Model – Option model | Minimum | – FX-linked notes
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Significant unobservable input, liabilities, percentage	0.03	0
FX volatility | Model – Option model | Minimum | Foreign exchange | FX options
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Significant unobservable input, assets, percentage	0.01	0
FX volatility | Model – Option model | Maximum | – FX-linked notes
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Significant unobservable input, liabilities, percentage	0.36	0.36
FX volatility | Model – Option model | Maximum | Foreign exchange | FX options
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Significant unobservable input, assets, percentage	0.36	0.43
Credit spread | Model – Discounted cash flow | Minimum | Derivatives with monolines
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Significant unobservable input, assets, percentage	0.02	0.02
Credit spread | Model – Discounted cash flow | Maximum | Derivatives with monolines
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Significant unobservable input, assets, percentage	0.02	0.02
IR volatility | Minimum | Interest rate | long-dated swaptions
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Significant unobservable input, liabilities, percentage		0.06
IR volatility | Maximum | Interest rate | long-dated swaptions
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Significant unobservable input, liabilities, percentage		0.28
IR volatility | Model – Option model | Minimum | Interest rate | long-dated swaptions
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Significant unobservable input, assets, percentage	0.06	0.06
IR volatility | Model – Option model | Maximum | Interest rate | long-dated swaptions
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Significant unobservable input, assets, percentage	0.25	0.28
IR volatility | Model – Discounted cash flow | Minimum | – repurchase agreements
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Significant unobservable input, assets, percentage	0	0
IR volatility | Model – Discounted cash flow | Maximum | – repurchase agreements
Disclosure Of Fair Value Measurement Of Assets And Liabilities [Line Items]
Significant unobservable input, assets, percentage	0.05	0.05