v3.20.4
Trading Cash Instruments - Cash Instruments, Level 3 Rollforward (Detail) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Trading Cash Instruments Assets [Member]    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value, Beginning Balance $ 1,242 $ 1,689
Net realized gains / (losses) 66 89
Net unrealized gains / (losses) (143) (35)
Purchases 796 522
Sales (411) (885)
Settlements (266) (252)
Transfers into level 3 156 256
Transfers out of level 3 (203) (142)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value, Ending Balance 1,237 1,242
Trading Cash Instruments Assets [Member] | Loans and Securities Backed by Commercial Real Estate [Member]    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value, Beginning Balance 191 332
Net realized gains / (losses) 11 5
Net unrealized gains / (losses) (33) (17)
Purchases 110 49
Sales (19) (153)
Settlements (64) (48)
Transfers into level 3 25 37
Transfers out of level 3 (18) (14)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value, Ending Balance 203 191
Trading Cash Instruments Assets [Member] | Loans and Securities Backed by Residential Real Estate [Member]    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value, Beginning Balance 231 348
Net realized gains / (losses) 11 14
Net unrealized gains / (losses) 23 28
Purchases 69 111
Sales (80) (223)
Settlements (40) (37)
Transfers into level 3 5 19
Transfers out of level 3 (88) (29)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value, Ending Balance 131 231
Trading Cash Instruments Assets [Member] | Corporate debt instruments [Member]    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value, Beginning Balance 692 912
Net realized gains / (losses) 47 58
Net unrealized gains / (losses) (118) (27)
Purchases 551 291
Sales (233) (458)
Settlements (146) (134)
Transfers into level 3 96 142
Transfers out of level 3 (92) (92)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value, Ending Balance 797 692
Trading Cash Instruments Assets [Member] | Other Cash Instruments [Member]    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value, Beginning Balance 128 97
Net realized gains / (losses) (3) 12
Net unrealized gains / (losses) (15) (19)
Purchases 66 71
Sales (79) (51)
Settlements (16) (33)
Transfers into level 3 30 58
Transfers out of level 3 (5) (7)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value, Ending Balance 106 128
Trading Cash Instruments Liabilities [Member]    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability Value, Beginning Balance (273) (49)
Net realized gains / (losses)   10
Net unrealized gains / (losses) (15) (236)
Purchases 34 56
Sales (38) (35)
Settlements 9  
Transfers into level 3 (27) (24)
Transfers out of level 3 230 5
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability Value, Ending Balance $ (80) $ (273)