Commitments and contingent liabilities - Narrative (Details)					2 Months Ended	9 Months Ended
	Aug. 04, 2021 claim investment_fund	May 20, 2021 USD ($)	Sep. 09, 2020 USD ($)	Dec. 17, 2015 lawsuit	Dec. 31, 2020 USD ($)	Sep. 30, 2021 USD ($) claim	Jun. 30, 2021 USD ($)	Sep. 30, 2020 USD ($)	Dec. 31, 2009 claim
Commitments and Contingencies Disclosure [Line Items]
Lending commitment maturing in less than one year						$ 28,000,000,000
Lending commitment maturing in one to five years						18,100,000,000
Lending commitment maturing over five years						787,000,000
Allowance for credit losses on lending related commitments					$ 121,000,000	$ 40,000,000	$ 50,000,000	$ 135,000,000
Collateralization percentage generally required for a securities lending transaction with indemnification against broker default						102.00%
Securities lending indemnifications, secured amount of collateral					493,000,000,000	$ 511,000,000,000
Securities lending indemnifications, joint venture					62,000,000,000	64,000,000,000
Securities lending indemnifications, collateral joint venture					66,000,000,000	68,000,000,000
Unsettled Repurchase Agreements
Commitments and Contingencies Disclosure [Line Items]
Unsettled repurchase and reverse repurchase agreements						3,700,000,000
Unsettled Reverse Repurchase Agreements
Commitments and Contingencies Disclosure [Line Items]
Unsettled repurchase and reverse repurchase agreements						$ 10,400,000,000
Mortgage-Securitization Trusts Proceedings | Federal Court
Commitments and Contingencies Disclosure [Line Items]
Number of lawsuits or class actions (claim) | claim						3
Mortgage-Securitization Trusts Proceedings | State Court
Commitments and Contingencies Disclosure [Line Items]
Number of lawsuits or class actions (claim) | claim						2
Matters Related to R. Allen Stanford
Commitments and Contingencies Disclosure [Line Items]
Number of lawsuits or class actions (claim) | claim									2
New claims filed, number | claim						3
Brazilian Postalis Litigation
Commitments and Contingencies Disclosure [Line Items]
New claims filed, number	3			3
Number of investment funds | investment_fund	3
Damages awarded, value		$ 3,000,000	$ 45,000,000
Damages sought, value			$ 2,000,000
German Tax Matters | Foreign Tax Authority
Commitments and Contingencies Disclosure [Line Items]
Damages sought, value					150,000,000
Maximum
Commitments and Contingencies Disclosure [Line Items]
Loss contingency, aggregate range of reasonable loss (up to)						$ 615,000,000
Standby letters of credit
Commitments and Contingencies Disclosure [Line Items]
Standby letters of credit (SBLC) collateralized with cash and securities					194,000,000	163,000,000
SBLC expiring within one year						1,400,000,000
SBLC expiring within one to five years						558,000,000
SBLC expiring over five years						0
Off-balance sheet credit risks					2,265,000,000	1,993,000,000
Commercial letters of credit
Commitments and Contingencies Disclosure [Line Items]
Off-balance sheet credit risks					$ 60,000,000	$ 146,000,000