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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, 2017 | Dec. 31, 2016
Accounts Notes And Loans Receivable [Line Items] |  |
Beginning balance, fair value assets | $ 1,552 | $ 1,834
Realized gains/(losses), assets |  | (1)
Unrealized gains/(losses) included in earnings, assets | 170 | (16)
Unrealized gains/(losses) included in OCI, assets | 2 | 32
Foreign exchange recognized in OCI or earnings, assets | (2) | 5
Purchases, assets | 737 | 278
Settlements, assets | (324) | (344)
Sales, assets | (3) | (109)
Transfers into level 3, assets | 31 | 17
Transfers out of level 3, assets | (23) | (144)
Ending balance, fair value assets | 2,140 | 1,552
Change in unrealized gains/(losses) for the period included in earnings for assets still held, assets | 168 | 8
Beginning balance, fair value liabilities | 661 | 1,531
Realized gains/(losses), liabilities | 51 | 43
Unrealized gains/(losses included in earnings, liabilities | 53 | (45)
Foreign exchange recognized in OCI or earnings, liabilities | 15 | (1)
Purchases, liabilities | 7 | 9
Settlements, liabilities | (141) | (245)
Sales, liabilities | (51) | (631)
Ending balance, fair value liabilities | 595 | 661
Change in unrealized gains/(losses) for the period included in earnings for liabilities still held, liabilities | 70 | (38)
Residential Prime Financing Receivable [Member] | Variable Interest Entity Primary Beneficiary [Member] |  |
Accounts Notes And Loans Receivable [Line Items] |  |
Beginning balance, fair value assets | 916 | 1,185
Unrealized gains/(losses) included in earnings, assets | 79 | (11)
Settlements, assets | (236) | (258)
Ending balance, fair value assets | 759 | 916
Change in unrealized gains/(losses) for the period included in earnings for assets still held, assets | 79 | (11)
Corporate Loans Receivable [Member] | Variable Interest Entity Primary Beneficiary [Member] |  |
Accounts Notes And Loans Receivable [Line Items] |  |
Beginning balance, fair value assets | 150 | 107
Unrealized gains/(losses) included in earnings, assets | 89 | 4
Purchases, assets | 719 | 146
Settlements, assets | (38) |
Sales, assets |  | (107)
Ending balance, fair value assets | 920 | 150
Change in unrealized gains/(losses) for the period included in earnings for assets still held, assets | 89 | 4
Loan Repurchase Commitments [Member] | Variable Interest Entity Primary Beneficiary [Member] |  |
Accounts Notes And Loans Receivable [Line Items] |  |
Beginning balance, fair value assets | 404 | 396
Unrealized gains/(losses) included in earnings, assets | 3 | 8
Ending balance, fair value assets | 407 | 404
Change in unrealized gains/(losses) for the period included in earnings for assets still held, assets | 3 | 8
State and municipal bonds [Member] |  |
Accounts Notes And Loans Receivable [Line Items] |  |
Beginning balance, fair value assets |  | 41
Purchases, assets |  | 122
Settlements, assets |  | (39)
Sales, assets |  | (1)
Transfers into level 3, assets | 1 | 2
Transfers out of level 3, assets | (1) | (125)
Foreign Government Debt [Member] |  |
Accounts Notes And Loans Receivable [Line Items] |  |
Beginning balance, fair value assets |  | 2
Foreign exchange recognized in OCI or earnings, assets |  | (1)
Purchases, assets |  | 10
Settlements, assets |  | (10)
Transfers out of level 3, assets |  | (1)
Corporate Obligations [Member] |  |
Accounts Notes And Loans Receivable [Line Items] |  |
Beginning balance, fair value assets | 2 | 7
Purchases, assets | 1 |
Transfers into level 3, assets |  | 2
Transfers out of level 3, assets | (1) | (7)
Ending balance, fair value assets | 2 | 2
Corporate Obligations [Member] | Variable Interest Entity Primary Beneficiary [Member] |  |
Accounts Notes And Loans Receivable [Line Items] |  |
Beginning balance, fair value assets |  | 11
Unrealized gains/(losses) included in earnings, assets |  | (6)
Settlements, assets | (2) | (2)
Transfers into level 3, assets | 6 | 2
Transfers out of level 3, assets | (4) | (5)
Residential Mortgage Backed Non Agency [Member] | Variable Interest Entity Primary Beneficiary [Member] |  |
Accounts Notes And Loans Receivable [Line Items] |  |
Unrealized gains/(losses) included in earnings, assets |  | (1)
Transfers into level 3, assets |  | 1
Commercial Mortgage Backed Securities [Member] |  |
Accounts Notes And Loans Receivable [Line Items] |  |
Sales, assets |  | (1)
Transfers into level 3, assets | 14 | 1
Transfers out of level 3, assets | (7) |
Ending balance, fair value assets | 7 |
Commercial Mortgage Backed Securities [Member] | Variable Interest Entity Primary Beneficiary [Member] |  |
Accounts Notes And Loans Receivable [Line Items] |  |
Unrealized gains/(losses) included in earnings, assets |  | (4)
Sales, assets | (3) |
Transfers into level 3, assets | 9 | 4
Ending balance, fair value assets | 6 |
Collateralized Debt Obligations [Member] |  |
Accounts Notes And Loans Receivable [Line Items] |  |
Beginning balance, fair value assets | 15 | 29
Unrealized gains/(losses) included in OCI, assets |  | 18
Settlements, assets | (7) | (32)
Transfers out of level 3, assets | (8) |
Ending balance, fair value assets |  | 15
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 | 44 | 38
Realized gains/(losses), assets |  | (1)
Unrealized gains/(losses) included in earnings, assets |  | (1)
Unrealized gains/(losses) included in OCI, assets | 2 | 14
Settlements, assets | (41) | (3)
Transfers out of level 3, assets |  | (3)
Ending balance, fair value assets | 5 | 44
Change in unrealized gains/(losses) for the period included in earnings for assets still held, assets |  | (1)
Other Asset Backed [Member] | Variable Interest Entity Primary Beneficiary [Member] |  |
Accounts Notes And Loans Receivable [Line Items] |  |
Beginning balance, fair value assets | 1 | 6
Unrealized gains/(losses) included in earnings, assets |  | (7)
Transfers into level 3, assets | 1 | 5
Transfers out of level 3, assets | (2) | (3)
Ending balance, fair value assets |  | 1
Medium Term Notes [Member] |  |
Accounts Notes And Loans Receivable [Line Items] |  |
Beginning balance, fair value liabilities | 101 | 161
Unrealized gains/(losses included in earnings, liabilities | (1) | (3)
Foreign exchange recognized in OCI or earnings, liabilities | 15 | (1)
Settlements, liabilities |  | (56)
Ending balance, fair value liabilities | 115 | 101
Change in unrealized gains/(losses) for the period included in earnings for liabilities still held, liabilities | 14 | (4)
Credit Derivatives [Member] |  |
Accounts Notes And Loans Receivable [Line Items] |  |
Beginning balance, fair value liabilities | 64 | 85
Realized gains/(losses), liabilities | 51 | 43
Unrealized gains/(losses included in earnings, liabilities | (1) | (21)
Settlements, liabilities | (51) | (43)
Ending balance, fair value liabilities | 63 | 64
Change in unrealized gains/(losses) for the period included in earnings for liabilities still held, liabilities | 1 | (13)
Other Derivative Liabilities [Member] |  |
Accounts Notes And Loans Receivable [Line Items] |  |
Beginning balance, fair value liabilities | 20 | 18
Unrealized gains/(losses included in earnings, liabilities | 18 | 2
Settlements, liabilities | (34) |
Ending balance, fair value liabilities | 4 | 20
Change in unrealized gains/(losses) for the period included in earnings for liabilities still held, liabilities | 18 | 2
Variable Interest Entity Notes [Member] | Variable Interest Entity Primary Beneficiary [Member] |  |
Accounts Notes And Loans Receivable [Line Items] |  |
Beginning balance, fair value liabilities | 476 | 1,267
Unrealized gains/(losses included in earnings, liabilities | 37 | (23)
Purchases, liabilities |  | 9
Settlements, liabilities | (56) | (146)
Sales, liabilities | (51) | (631)
Ending balance, fair value liabilities | 406 | 476
Change in unrealized gains/(losses) for the period included in earnings for liabilities still held, liabilities | 37 | (23)
Currency Derivatives [Member] | Variable Interest Entity Primary Beneficiary [Member] |  |
Accounts Notes And Loans Receivable [Line Items] |  |
Beginning balance, fair value assets | 19 | 11
Unrealized gains/(losses) included in earnings, assets | 2 | 2
Foreign exchange recognized in OCI or earnings, assets | (2) | 6
Ending balance, fair value assets | 19 | 19
Change in unrealized gains/(losses) for the period included in earnings for assets still held, assets | 0 | $ 8
Other Assets [Member] | Variable Interest Entity Primary Beneficiary [Member] |  |
Accounts Notes And Loans Receivable [Line Items] |  |
Unrealized gains/(losses) included in earnings, assets | (3) |
Purchases, assets | 17 |
Ending balance, fair value assets | 14 |
Change in unrealized gains/(losses) for the period included in earnings for assets still held, assets | (3) |
Other Payable [Member] |  |
Accounts Notes And Loans Receivable [Line Items] |  |
Unrealized gains/(losses included in earnings, liabilities | 0 |
Purchases, liabilities | 7 |
Ending balance, fair value liabilities | 7 |
Change in unrealized gains/(losses) for the period included in earnings for liabilities still held, liabilities | $ 0 |

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