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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
--- | ---
Mar. 31, 2018 | Mar. 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 | 28 | 1
Unrealized gains/(losses) included in OCI, assets | 0 | 2
Foreign exchange recognized in OCI or earnings, assets | (3) | (3)
Purchases, assets | 2 | 719
Issuances, assets | 0 | 0
Settlements, assets | (49) | (111)
Sales, assets | (2) | 0
Transfers into level 3, assets | 3 | 8
Transfers out of level 3, assets | (2) | (3)
Ending balance, fair value assets | 2,117 | 2,165
Change in unrealized gains/(losses) for the period included in earnings for assets still held, assets | 25 | (1)
Beginning balance, fair value liabilities | 595 | 661
Realized gains/(losses), liabilities | 27 | 31
Unrealized gains/(losses included in earnings, liabilities | (15) | 57
Unrealized gains/(losses) included in OCI, liabilities | 17 | 0
Foreign exchange recognized in OCI or earnings, liabilities | 11 | 2
Purchases, liabilities | 0 | 0
Issuances, liabilities | 5 | 0
Settlements, liabilities | (36) | (50)
Sales, liabilities | 0 | 0
Transfers into Level 3, liabilities | 0 | 0
Transfers out of Level 3, liabilities | 0 | 0
Ending balance, fair value liabilities | 604 | 701
Change in unrealized gains/(losses) for the period included in earnings for liabilities still held, liabilities | (4) | 59
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 | 20 | (4)
Settlements, assets | (42) | (68)
Ending balance, fair value assets | 737 | 844
Change in unrealized gains/(losses) for the period included in earnings for assets still held, assets | 20 | (3)
Corporate Loans Receivable [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 | 3
Purchases, assets |  | 719
Settlements, assets | (6) |
Ending balance, fair value assets | 925 | 872
Change in unrealized gains/(losses) for the period included in earnings for assets still held, assets | 11 | 3
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 |  | 5
Ending balance, fair value assets | 407 | 409
Change in unrealized gains/(losses) for the period included in earnings for assets still held, assets |  | 5
State and municipal bonds [Member] |  |
Accounts Notes And Loans Receivable [Line Items] |  |
Transfers into level 3, assets |  | 1
Ending balance, fair value assets |  | 1
Corporate Obligations [Member] |  |
Accounts Notes And Loans Receivable [Line Items] |  |
Beginning balance, fair value assets | 2 | 2
Transfers out of level 3, assets | (2) | (2)
Corporate Obligations [Member] | Variable Interest Entity Primary Beneficiary [Member] |  |
Accounts Notes And Loans Receivable [Line Items] |  |
Transfers into level 3, assets | 3 | 6
Ending balance, fair value assets | 3 | 6
Commercial Mortgage Backed Securities [Member] |  |
Accounts Notes And Loans Receivable [Line Items] |  |
Beginning balance, fair value 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] |  |
Beginning balance, fair value 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 |  | (2)
Ending balance, fair value assets |  | 13
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 |  | 2
Purchases, assets | 2 |
Settlements, assets | (1) | (41)
Sales, assets | (2) |
Ending balance, fair value assets | 4 | 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 |  | (1)
Ending balance, fair value assets |  | 1
Medium Term Notes [Member] |  |
Accounts Notes And Loans Receivable [Line Items] |  |
Beginning balance, fair value liabilities | 115 | 101
Unrealized gains/(losses included in earnings, liabilities |  | 1
Unrealized gains/(losses) included in OCI, liabilities | 25 |
Foreign exchange recognized in OCI or earnings, liabilities | 6 | 2
Ending balance, fair value liabilities | 146 | 104
Change in unrealized gains/(losses) for the period included in earnings for liabilities still held, liabilities | 6 | 3
Credit Derivatives [Member] |  |
Accounts Notes And Loans Receivable [Line Items] |  |
Beginning balance, fair value liabilities | 63 | 64
Realized gains/(losses), liabilities | 19 | 31
Unrealized gains/(losses included in earnings, liabilities | (14) | 22
Settlements, liabilities | (19) | (31)
Ending balance, fair value liabilities | 49 | 86
Change in unrealized gains/(losses) for the period included in earnings for liabilities still held, liabilities | (14) | 22
Other Derivative Liabilities [Member] |  |
Accounts Notes And Loans Receivable [Line Items] |  |
Beginning balance, fair value liabilities | 4 | 20
Ending balance, fair value liabilities | 4 | 20
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 | 8 |
Unrealized gains/(losses included in earnings, liabilities | (3) | 34
Unrealized gains/(losses) included in OCI, liabilities | (8) |
Foreign exchange recognized in OCI or earnings, liabilities | 5 |
Issuances, liabilities | 5 |
Settlements, liabilities | (13) | (19)
Ending balance, fair value liabilities | 400 | 491
Change in unrealized gains/(losses) for the period included in earnings for liabilities still held, liabilities | 2 | 34
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 | (3) | (3)
Foreign exchange recognized in OCI or earnings, assets | (3) | (3)
Ending balance, fair value assets | 13 | 13
Change in unrealized gains/(losses) for the period included in earnings for assets still held, assets | (6) | $ (6)
Other Assets [Member] | Variable Interest Entity Primary Beneficiary [Member] |  |
Accounts Notes And Loans Receivable [Line Items] |  |
Beginning balance, fair value assets | 14 |
Ending balance, fair value assets | 14 |
Other Payable [Member] |  |
Accounts Notes And Loans Receivable [Line Items] |  |
Beginning balance, fair value liabilities | 7 |
Unrealized gains/(losses included in earnings, liabilities | 2 |
Settlements, liabilities | (4) |
Ending balance, fair value liabilities | 5 |
Change in unrealized gains/(losses) for the period included in earnings for liabilities still held, liabilities | $ 2 |

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