Loans and Allowance for Credit Losses - Net Loans (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Dec. 31, 2018
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, gross	$ 27,035	$ 26,309
Allowance for loan losses	(134)	(74)	$ (71)	$ (72)	$ (67)
Loans, net of allowance	26,901	26,235
Loans, Excluding Unfunded Commitments
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, gross	27,035	26,309
Allowance for loan losses	(134)	(74)
Loans, net of allowance	26,901	26,235
Fund Finance | Securities Finance Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, gross	1,859	2,537
Fund Finance | Municipal Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, gross	850	848
Fund Finance | Other Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, gross	55	26
Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, gross	1,944	1,766
Domestic
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, gross	19,952	20,528
Domestic | Fund Finance
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, gross	10,012	10,270
Overdrafts	3,793	3,256
Domestic | Fund Finance | 40 Act Funds
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, gross	5,345	6,040
Domestic | Fund Finance | Private Equity Capital Call Finance Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, gross	7,654	6,076
Domestic | Fund Finance | Business Development
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, gross	860	932
Domestic | Leveraged loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, gross	3,038	3,342
Domestic | Overdrafts
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, gross	2,223	1,739
Domestic | Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, gross	2,735	3,411
Domestic | Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, gross	1,944	1,766
Foreign
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, gross	7,083	5,781
Foreign | Fund Finance
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, gross	4,262	3,145
Foreign | Leveraged loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, gross	1,222	1,119
Foreign | Overdrafts
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, gross	1,570	1,517
Foreign | Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, gross	$ 29	$ 0