Credit Concentrations - Credit Concentration, Government and Federal Agency Obligations (Detail) - USD ($) $ in Millions |
12 Months Ended | |
|---|---|---|
Dec. 31, 2020 |
Dec. 31, 2019 |
|
| U.S. Government and Agency Obligations Held By The Firm [Member] | ||
| Concentration Risk [Line Items] | ||
| Concentration risk, Credit risk, Financial instrument, Maximum exposure | $ 187,009 | $ 167,097 |
| Concentration risk, Credit risk, Financial instrument, Maximum exposure, As a percentage of total Assets | 16.10% | 16.80% |
| Non-U.S. Government and Agency Obligations Held By The Firm [Member] | ||
| Concentration Risk [Line Items] | ||
| Concentration risk, Credit risk, Financial instrument, Maximum exposure | $ 59,580 | $ 44,875 |
| Concentration risk, Credit risk, Financial instrument, Maximum exposure, As a percentage of total Assets | 5.10% | 4.50% |