v3.20.4
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%