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Fair Value Of Financial Instruments (Changes In Level 3 Assets And Liabilities Measured At Fair Value On A Recurring Basis) (Detail) - Fair Value Inputs Level 3 [Member] - USD ($) $ in Millions | 3 Months Ended | 6 Months Ended
--- | --- | ---
Jun. 30, 2019 | Jun. 30, 2018 | Jun. 30, 2019 | Jun. 30, 2018
Accounts Notes And Loans Receivable [Line Items] |  |  |  |
Beginning balance, fair value assets | $ 669 | $ 2,117 | $ 637 | $ 2,140
Realized gains/(losses), assets | (1) | 0 | (1) | 0
Unrealized gains/(losses) included in earnings, assets | 6 | (8) | 49 | 20
Unrealized gains/(losses) included in OCI, assets | 0 | 0 | 0 | 0
Foreign exchange recognized in OCI or earnings, assets | 0 | 3 | (1) | 0
Purchases, assets | 0 | 2 | 0 | 5
Issuances, assets | 0 | 0 | 0 | 0
Settlements, assets | (9) | (41) | (19) | (90)
Sales, assets | (49) | (925) | (49) | (928)
Transfers into level 3, assets | 0 | 3 | 0 | 6
Transfers out of level 3, assets | (3) | (13) | (3) | (15)
Ending balance, fair value assets | 613 | 1,138 | 613 | 1,138
Change in unrealized gains/(losses) for the period included in earnings for assets still held, assets | 4 | (5) | 43 | 9
Beginning balance, fair value liabilities | 532 | 604 | 513 | 595
Realized gains/(losses), liabilities | (1) | 29 | 8 | 56
Unrealized gains/(losses included in earnings, liabilities | 14 | (31) | 43 | (46)
Unrealized gains/(losses) included in OCI, liabilities | 9 | 24 | (1) | 41
Foreign exchange recognized in OCI or earnings, liabilities | 3 | (18) | 1 | (8)
Purchases, liabilities | 0 | 0 | 0 | 0
Issuances, liabilities | 0 | 1 | 4 | 6
Settlements, liabilities | (8) | (31) | (19) | (66)
Sales, liabilities | (60) | 0 | (60) | 0
Transfers into Level 3, liabilities | 0 | 0 | 0 | 0
Transfers out of Level 3, liabilities | 0 | 0 | 0 | 0
Ending balance, fair value liabilities | 489 | 578 | 489 | 578
Change in unrealized gains/(losses) for the period included in earnings for liabilities still held, liabilities | 17 | (49) | 43 | (54)
Residential Prime Financing Receivable [Member] | Variable Interest Entity Primary Beneficiary [Member] |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |
Beginning balance, fair value assets | 206 | 737 | 172 | 759
Unrealized gains/(losses) included in earnings, assets | 1 | (14) | 43 | 6
Settlements, assets | (5) | (40) | (13) | (82)
Sales, assets | (48) |  | (48) |
Ending balance, fair value assets | 154 | 683 | 154 | 683
Change in unrealized gains/(losses) for the period included in earnings for assets still held, assets | (1) | (14) | 38 | 6
Corporate Loans Receivable and Other Instruments [Member] | Variable Interest Entity Primary Beneficiary [Member] |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |
Beginning balance, fair value assets |  | 925 |  | 920
Unrealized gains/(losses) included in earnings, assets |  |  |  | 11
Settlements, assets |  |  |  | (6)
Sales, assets |  | (925) |  | (925)
Ending balance, fair value assets |  | 0 |  | 0
Loan Repurchase Commitments [Member] | Variable Interest Entity Primary Beneficiary [Member] |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |
Beginning balance, fair value assets | 420 | 407 | 418 | 407
Unrealized gains/(losses) included in earnings, assets | 8 | 8 | 10 | 8
Ending balance, fair value assets | 428 | 415 | 428 | 415
Change in unrealized gains/(losses) for the period included in earnings for assets still held, assets | 8 | 8 | 10 | 8
Corporate Obligations [Member] |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |
Beginning balance, fair value assets |  |  |  | 2
Transfers out of level 3, assets |  |  |  | (2)
Ending balance, fair value assets |  | 0 |  | 0
Corporate Obligations [Member] | Variable Interest Entity Primary Beneficiary [Member] |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |
Beginning balance, fair value assets | 5 | 3 | 5 |
Settlements, assets | (2) | (1) | (2) | (1)
Transfers into level 3, assets |  | 3 |  | 6
Transfers out of level 3, assets | (3) |  | (3) |
Ending balance, fair value assets | 0 | 5 | 0 | 5
Commercial Mortgage Backed Securities [Member] |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |
Beginning balance, fair value assets | 6 | 7 | 7 | 7
Settlements, assets | (2) |  | (3) |
Transfers out of level 3, assets |  | (7) |  | (7)
Ending balance, fair value assets | 4 | 0 | 4 | 0
Commercial Mortgage Backed Securities [Member] | Variable Interest Entity Primary Beneficiary [Member] |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |
Beginning balance, fair value assets |  | 6 |  | 6
Transfers out of level 3, assets |  | (6) |  | (6)
Ending balance, fair value assets |  | 0 |  | 0
Collateralized Debt Obligations [Member] | Variable Interest Entity Primary Beneficiary [Member] |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |
Beginning balance, fair value assets | 1 | 1 | 1 | 1
Sales, assets | (1) |  | (1) |
Transfers out of level 3, assets |  |  |  | 0
Ending balance, fair value assets | 0 | 1 | 0 | 1
Other Asset Backed [Member] |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |
Beginning balance, fair value assets | 2 | 4 | 3 | 5
Realized gains/(losses), assets | (1) |  | (1) |
Purchases, assets |  | 2 |  | 5
Settlements, assets |  |  | (1) | (1)
Sales, assets |  |  |  | (3)
Ending balance, fair value assets | 1 | 6 | 1 | 6
Medium Term Notes [Member] |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |
Beginning balance, fair value liabilities | 106 | 146 | 102 | 115
Unrealized gains/(losses included in earnings, liabilities | (5) | (1) | 5 |
Unrealized gains/(losses) included in OCI, liabilities | 10 | 15 | 6 | 40
Foreign exchange recognized in OCI or earnings, liabilities | 2 | (11) |  | (6)
Settlements, liabilities | (3) |  | (3) |
Ending balance, fair value liabilities | 110 | 149 | 110 | 149
Change in unrealized gains/(losses) for the period included in earnings for liabilities still held, liabilities | (2) | (12) | 4 | (6)
Credit Derivatives [Member] |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |
Beginning balance, fair value liabilities | 19 | 49 | 33 | 63
Realized gains/(losses), liabilities | 1 | 25 | 1 | 44
Unrealized gains/(losses included in earnings, liabilities |  | (18) | (14) | (32)
Settlements, liabilities | (2) | (25) | (2) | (44)
Ending balance, fair value liabilities | 18 | 31 | 18 | 31
Change in unrealized gains/(losses) for the period included in earnings for liabilities still held, liabilities |  | (18) | (14) | (32)
Other Derivatives Liabilities [Member] |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |
Beginning balance, fair value liabilities | 7 | 4 | 7 | 4
Unrealized gains/(losses included in earnings, liabilities | 9 |  | 9 |
Ending balance, fair value liabilities | 16 | 4 | 16 | 4
Change in unrealized gains/(losses) for the period included in earnings for liabilities still held, liabilities | 9 |  | 9 |
Variable Interest Entity Notes [Member] | Liabilities Of Consolidated Vies [Member] |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |
Beginning balance, fair value liabilities | 397 | 400 | 366 | 406
Realized gains/(losses), liabilities | (2) | 4 | 7 | 12
Unrealized gains/(losses included in earnings, liabilities | 10 | (12) | 42 | (16)
Unrealized gains/(losses) included in OCI, liabilities | (1) | 9 | (7) | 1
Foreign exchange recognized in OCI or earnings, liabilities | 1 | (7) | 1 | (2)
Issuances, liabilities |  | 1 | 4 | 6
Settlements, liabilities | (3) | (6) | (11) | (18)
Sales, liabilities | (60) |  | (60) |
Ending balance, fair value liabilities | 342 | 389 | 342 | 389
Change in unrealized gains/(losses) for the period included in earnings for liabilities still held, liabilities | 10 | (19) | 43 | (18)
Currency Derivatives [Member] | Variable Interest Entity Primary Beneficiary [Member] |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |
Beginning balance, fair value assets | 14 | 13 | 17 | 19
Unrealized gains/(losses) included in earnings, assets | (3) | (2) | (5) | (5)
Foreign exchange recognized in OCI or earnings, assets |  | 3 | (1) |
Ending balance, fair value assets | 11 | 14 | 11 | 14
Change in unrealized gains/(losses) for the period included in earnings for assets still held, assets | (3) | 1 | (6) | (5)
Other Assets [Member] | Variable Interest Entity Primary Beneficiary [Member] |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |
Beginning balance, fair value assets | 15 | 14 | 14 | 14
Unrealized gains/(losses) included in earnings, assets |  | 0 | 1 | 0
Foreign exchange recognized in OCI or earnings, assets |  | 0 |  |
Ending balance, fair value assets | 15 | 14 | 15 | 14
Change in unrealized gains/(losses) for the period included in earnings for assets still held, assets |  |  | 1 |
Other Payable [Member] |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |
Beginning balance, fair value liabilities | 3 | 5 | 5 | 7
Unrealized gains/(losses included in earnings, liabilities |  |  | 1 | 2
Settlements, liabilities |  |  | (3) | (4)
Ending balance, fair value liabilities | $ 3 | $ 5 | 3 | 5
Change in unrealized gains/(losses) for the period included in earnings for liabilities still held, liabilities |  |  | $ 1 | $ 2

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