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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 | 12 Months Ended
--- | ---
Dec. 31, 2018 | Dec. 31, 2017
Accounts Notes And Loans Receivable [Line Items] |  |
Beginning balance, fair value assets | $ 2,140 | $ 1,552
Realized gains/(losses), assets | 0 | 0
Unrealized gains/(losses) included in earnings, assets | 34 | 170
Unrealized gains/(losses) included in OCI, assets | (1) | 2
Foreign exchange recognized in OCI or earnings, assets | 0 | (2)
Purchases, assets | 5 | 737
Issuances, assets | 0 | 0
Settlements, assets | (122) | (324)
Sales, assets | (1,415) | (3)
Transfers into level 3, assets | 13 | 31
Transfers out of level 3, assets | (17) | (23)
Ending balance, fair value assets | 637 | 2,140
Change in unrealized gains/(losses) for the period included in earnings for assets still held, assets | (13) | 168
Beginning balance, fair value liabilities | 595 | 661
Realized gains/(losses), liabilities | 86 | 51
Unrealized gains/(losses included in earnings, liabilities | (57) | 53
Unrealized gains/(losses) included in OCI, liabilities | 35 | 0
Foreign exchange recognized in OCI or earnings, liabilities | (10) | 15
Purchases, liabilities | 0 | 7
Issuances, liabilities | 8 | 0
Settlements, liabilities | (144) | (141)
Sales, liabilities | 0 | (51)
Transfers into Level 3, liabilities | 0 | 0
Transfers out of Level 3, liabilities | 0 | 0
Ending balance, fair value liabilities | 513 | 595
Change in unrealized gains/(losses) for the period included in earnings for liabilities still held, liabilities | (67) | 70
Residential Prime Financing Receivable [Member] | Variable Interest Entity Primary Beneficiary [Member] |  |
Accounts Notes And Loans Receivable [Line Items] |  |
Beginning balance, fair value assets | 759 | 916
Unrealized gains/(losses) included in earnings, assets | 14 | 79
Settlements, assets | (114) | (236)
Sales, assets | (487) |
Ending balance, fair value assets | 172 | 759
Change in unrealized gains/(losses) for the period included in earnings for assets still held, assets | (22) | 79
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 | 920 | 150
Unrealized gains/(losses) included in earnings, assets | 11 | 89
Purchases, assets |  | 719
Settlements, assets | (6) | (38)
Sales, assets | (925) |
Ending balance, fair value assets |  | 920
Change in unrealized gains/(losses) for the period included in earnings for assets still held, assets |  | 89
Loan Repurchase Commitments [Member] | Variable Interest Entity Primary Beneficiary [Member] |  |
Accounts Notes And Loans Receivable [Line Items] |  |
Beginning balance, fair value assets | 407 | 404
Unrealized gains/(losses) included in earnings, assets | 11 | 3
Ending balance, fair value assets | 418 | 407
Change in unrealized gains/(losses) for the period included in earnings for assets still held, assets | 11 | 3
State and municipal bonds [Member] |  |
Accounts Notes And Loans Receivable [Line Items] |  |
Transfers into level 3, assets |  | 1
Transfers out of level 3, assets |  | (1)
Corporate Obligations [Member] |  |
Accounts Notes And Loans Receivable [Line Items] |  |
Beginning balance, fair value assets | 2 | 2
Purchases, assets |  | 1
Transfers out of level 3, assets | (2) | (1)
Ending balance, fair value assets |  | 2
Corporate Obligations [Member] | Variable Interest Entity Primary Beneficiary [Member] |  |
Accounts Notes And Loans Receivable [Line Items] |  |
Settlements, assets | (1) | (2)
Transfers into level 3, assets | 6 | 6
Transfers out of level 3, assets |  | (4)
Ending balance, fair value assets | 5 |
Commercial Mortgage Backed Securities [Member] |  |
Accounts Notes And Loans Receivable [Line Items] |  |
Beginning balance, fair value assets | 7 |
Transfers into level 3, assets | 7 | 14
Transfers out of level 3, assets | (7) | (7)
Ending balance, fair value assets | 7 | 7
Commercial Mortgage Backed Securities [Member] | Variable Interest Entity Primary Beneficiary [Member] |  |
Accounts Notes And Loans Receivable [Line Items] |  |
Beginning balance, fair value assets | 6 |
Sales, assets |  | (3)
Transfers into level 3, assets |  | 9
Transfers out of level 3, assets | (6) |
Ending balance, fair value assets |  | 6
Collateralized Debt Obligations [Member] |  |
Accounts Notes And Loans Receivable [Line Items] |  |
Beginning balance, fair value assets |  | 15
Settlements, assets |  | (7)
Transfers out of level 3, assets |  | (8)
Collateralized Debt Obligations [Member] | Variable Interest Entity Primary Beneficiary [Member] |  |
Accounts Notes And Loans Receivable [Line Items] |  |
Beginning balance, fair value assets | 1 | 1
Ending balance, fair value assets | 1 | 1
Other Asset Backed [Member] |  |
Accounts Notes And Loans Receivable [Line Items] |  |
Beginning balance, fair value assets | 5 | 44
Unrealized gains/(losses) included in OCI, assets | (1) | 2
Purchases, assets | 5 |
Settlements, assets | (1) | (41)
Sales, assets | (3) |
Transfers out of level 3, assets | (2) |
Ending balance, fair value assets | 3 | 5
Other Asset Backed [Member] | Variable Interest Entity Primary Beneficiary [Member] |  |
Accounts Notes And Loans Receivable [Line Items] |  |
Beginning balance, fair value assets |  | 1
Transfers into level 3, assets |  | 1
Transfers out of level 3, assets |  | (2)
Medium Term Notes [Member] |  |
Accounts Notes And Loans Receivable [Line Items] |  |
Beginning balance, fair value liabilities | 115 | 101
Realized gains/(losses), liabilities | (9) |
Unrealized gains/(losses included in earnings, liabilities | (1) | (1)
Unrealized gains/(losses) included in OCI, liabilities | 55 |
Foreign exchange recognized in OCI or earnings, liabilities | (10) | 15
Settlements, liabilities | (48) |
Ending balance, fair value liabilities | 102 | 115
Change in unrealized gains/(losses) for the period included in earnings for liabilities still held, liabilities | (11) | 14
Credit Derivatives [Member] |  |
Accounts Notes And Loans Receivable [Line Items] |  |
Beginning balance, fair value liabilities | 63 | 64
Realized gains/(losses), liabilities | 56 | 51
Unrealized gains/(losses included in earnings, liabilities | (30) | (1)
Settlements, liabilities | (56) | (51)
Ending balance, fair value liabilities | 33 | 63
Change in unrealized gains/(losses) for the period included in earnings for liabilities still held, liabilities | (30) | 1
Other Derivative Liabilities [Member] |  |
Accounts Notes And Loans Receivable [Line Items] |  |
Beginning balance, fair value liabilities | 4 | 20
Unrealized gains/(losses included in earnings, liabilities | 3 | 18
Settlements, liabilities |  | (34)
Ending balance, fair value liabilities | 7 | 4
Change in unrealized gains/(losses) for the period included in earnings for liabilities still held, liabilities | 3 | 18
Variable Interest Entity Notes [Member] | Variable Interest Entity Primary Beneficiary [Member] |  |
Accounts Notes And Loans Receivable [Line Items] |  |
Beginning balance, fair value liabilities | 406 | 476
Realized gains/(losses), liabilities | 39 |
Unrealized gains/(losses included in earnings, liabilities | (30) | 37
Unrealized gains/(losses) included in OCI, liabilities | (20) |
Foreign exchange recognized in OCI or earnings, liabilities | 0 |
Issuances, liabilities | 8 |
Settlements, liabilities | (37) | (56)
Sales, liabilities |  | (51)
Ending balance, fair value liabilities | 366 | 406
Change in unrealized gains/(losses) for the period included in earnings for liabilities still held, liabilities | (30) | 37
Currency Derivatives [Member] | Variable Interest Entity Primary Beneficiary [Member] |  |
Accounts Notes And Loans Receivable [Line Items] |  |
Beginning balance, fair value assets | 19 | 19
Unrealized gains/(losses) included in earnings, assets | (2) | 2
Foreign exchange recognized in OCI or earnings, assets | 0 | (2)
Ending balance, fair value assets | 17 | 19
Change in unrealized gains/(losses) for the period included in earnings for assets still held, assets | (2) | 0
Other Assets [Member] | Variable Interest Entity Primary Beneficiary [Member] |  |
Accounts Notes And Loans Receivable [Line Items] |  |
Beginning balance, fair value assets | 14 |
Unrealized gains/(losses) included in earnings, assets | 0 | (3)
Purchases, assets |  | 17
Ending balance, fair value assets | 14 | 14
Change in unrealized gains/(losses) for the period included in earnings for assets still held, assets | 0 | (3)
Other Payable [Member] |  |
Accounts Notes And Loans Receivable [Line Items] |  |
Beginning balance, fair value liabilities | 7 |
Unrealized gains/(losses included in earnings, liabilities | 1 | 0
Purchases, liabilities |  | 7
Settlements, liabilities | (3) |
Ending balance, fair value liabilities | 5 | 7
Change in unrealized gains/(losses) for the period included in earnings for liabilities still held, liabilities | $ 1 | $ 0

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