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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, 2017 | Mar. 31, 2016
Accounts Notes And Loans Receivable [Line Items] |  |  |
Beginning balance, fair value assets |  | $ 1,552 | $ 1,834
Realized gains/(losses), assets |  | 0 | (1)
Unrealized gains/(losses) included in earnings, assets |  | 1 | (29)
Unrealized gains/(losses) included in OCI, assets |  | 2 | 5
Foreign exchange recognized in OCI or earnings, assets |  | (3) | 0
Purchases, assets |  | 719 | 146
Issuances, assets |  | 0 | 0
Settlements, assets |  | (111) | (99)
Sales, assets |  | 0 | 0
Transfers into level 3, assets | [1] | 8 | 5
Transfers out of level 3, assets | [1] | (3) | (11)
Ending balance, fair value assets |  | 2,165 | 1,850
Change in unrealized gains/(losses) for the period included in earnings for assets still held, assets |  | (1) | (18)
Beginning balance, fair value liabilities |  | 661 | 1,531
Realized gains/(losses), liabilities |  | 31 | 14
Unrealized gains/(losses included in earnings, liabilities |  | 57 | (10)
Unrealized gains/(losses) included in OCI, liabilities |  | 0 | 0
Foreign exchange recognized in OCI or earnings, liabilities |  | 2 | 7
Purchases, liabilities |  | 0 | 9
Issuances, liabilities |  | 0 | 0
Settlements, liabilities |  | (50) | (92)
Sales, liabilities |  | 0 | 0
Transfers into Level 3, liabilities | [1] | 0 | 0
Transfers out of Level 3, liabilities | [1] | 0 | 0
Ending balance, fair value liabilities |  | 701 | 1,459
Change in unrealized gains/(losses) for the period included in earnings for liabilities still held, liabilities |  | 59 | 0
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 |  | (4) | (14)
Settlements, assets |  | (68) | (56)
Ending balance, fair value assets |  | 844 | 1,115
Change in unrealized gains/(losses) for the period included in earnings for assets still held, assets |  | (3) | (14)
Other 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 |  | 3 |
Purchases, assets |  | 719 | 146
Ending balance, fair value assets |  | 872 | 253
Change in unrealized gains/(losses) for the period included in earnings for assets still held, assets |  | 3 |
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 |  | 5 | 3
Ending balance, fair value assets |  | 409 | 399
Change in unrealized gains/(losses) for the period included in earnings for assets still held, assets |  | 5 | 3
State and municipal bonds [Member] |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |
Beginning balance, fair value assets |  | 0 | 41
Settlements, assets |  |  | (38)
Transfers into level 3, assets | [1] | 1 |
Transfers out of level 3, assets |  | 0 |
Ending balance, fair value assets |  | 1 | 3
Foreign Government Debt [Member] |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |
Beginning balance, fair value assets |  | 0 | 2
Purchases, assets |  | 0 |
Settlements, assets |  | 0 |
Ending balance, fair value assets |  | 0 | 2
Corporate Obligations [Member] |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |
Beginning balance, fair value assets |  | 2 | 7
Settlements, assets |  | 0 |
Transfers out of level 3, assets |  | (2) | (6)
Ending balance, fair value assets |  | 0 | 1
Corporate Obligations [Member] | Variable Interest Entity Primary Beneficiary [Member] |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |
Beginning balance, fair value assets |  | 0 | 11
Unrealized gains/(losses) included in earnings, assets |  |  | (5)
Transfers into level 3, assets |  | 6 |
Transfers out of level 3, assets | [1] |  | (5)
Ending balance, fair value assets |  | 6 | 1
Residential Mortgage Backed Non Agency [Member] | Variable Interest Entity Primary Beneficiary [Member] |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |
Beginning balance, fair value assets |  | 0 |
Unrealized gains/(losses) included in earnings, assets |  | 0 |
Commercial Mortgage Backed Securities [Member] |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |
Transfers into level 3, assets |  | 0 |
Ending balance, fair value assets |  | 0 |
Commercial Mortgage Backed Securities [Member] | Variable Interest Entity Primary Beneficiary [Member] |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |
Beginning balance, fair value assets |  | 0 |
Unrealized gains/(losses) included in earnings, assets |  | 0 |
Transfers into level 3, assets |  | 0 | 2
Ending balance, fair value assets |  | 0 | 2
Change in unrealized gains/(losses) for the period included in earnings for assets still held, assets |  | 0 |
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 |  |  | 0
Settlements, assets |  | (2) | (3)
Ending balance, fair value assets |  | 13 | 26
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 | 5
Settlements, assets |  | (41) | (2)
Transfers out of level 3, assets | [1] | 0 |
Ending balance, fair value assets |  | 5 | 39
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 |  |  | (6)
Transfers into level 3, assets |  | 1 | 3
Transfers out of level 3, assets |  | (1) |
Ending balance, fair value assets |  | 1 | 3
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 |  | 2 | 7
Settlements, liabilities |  | 0 |
Ending balance, fair value liabilities |  | 104 | 165
Change in unrealized gains/(losses) for the period included in earnings for liabilities still held, liabilities |  | 3 | 5
Credit Derivatives [Member] |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |
Beginning balance, fair value liabilities |  | 64 | 85
Realized gains/(losses), liabilities |  | 31 | 14
Unrealized gains/(losses included in earnings, liabilities |  | 22 | 14
Settlements, liabilities |  | (31) | (14)
Ending balance, fair value liabilities |  | 86 | 99
Change in unrealized gains/(losses) for the period included in earnings for liabilities still held, liabilities |  | 22 | 16
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 |  | 0 | 1
Ending balance, fair value liabilities |  | 20 | 19
Change in unrealized gains/(losses) for the period included in earnings for liabilities still held, liabilities |  | 0 | 1
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 |  | 34 | (22)
Purchases, liabilities |  |  | 9
Settlements, liabilities |  | (19) | (78)
Ending balance, fair value liabilities |  | 491 | 1,176
Change in unrealized gains/(losses) for the period included in earnings for liabilities still held, liabilities |  | 34 | (22)
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 |  | (3) | (6)
Foreign exchange recognized in OCI or earnings, assets |  | (3) |
Ending balance, fair value assets |  | 13 | 5
Change in unrealized gains/(losses) for the period included in earnings for assets still held, assets |  | $ (6) | $ (6)
[1] | Transferred in and out at the end of the period.

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