Commitments and contingent liabilities - Significant Industry Concentrations Related to Credit Exposure (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Loans	$ 64,328	$ 56,469
Financial institutions
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Loans	9,400
Unfunded commitments	32,100
Total exposure	41,500
Financial institutions | Securities industry
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Loans	2,000
Unfunded commitments	18,800
Total exposure	20,800
Financial institutions | Asset managers
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Loans	1,500
Unfunded commitments	7,400
Total exposure	8,900
Financial institutions | Banks
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Loans	4,900
Unfunded commitments	1,700
Total exposure	6,600
Financial institutions | Insurance
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Loans	300
Unfunded commitments	3,000
Total exposure	3,300
Financial institutions | Government
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Loans	100
Unfunded commitments	100
Total exposure	200
Financial institutions | Other
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Loans	600
Unfunded commitments	1,100
Total exposure	1,700
Commercial
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Loans	1,700
Unfunded commitments	11,900
Total exposure	13,600
Commercial | Manufacturing
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Loans	500
Unfunded commitments	4,000
Total exposure	4,500
Commercial | Energy and utilities
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Loans	300
Unfunded commitments	3,900
Total exposure	4,200
Commercial | Services and other
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Loans	800
Unfunded commitments	3,200
Total exposure	4,000
Commercial | Media and telecom
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Loans	100
Unfunded commitments	800
Total exposure	$ 900