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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, 2016 | Mar. 31, 2015
Accounts Notes And Loans Receivable [Line Items] |  |  |
Beginning balance, fair value assets |  | $ 1,834 | $ 2,097
Realized gains/(losses), assets |  | (1) | (2)
Unrealized gains/(losses) included in earnings, assets |  | (29) | 10
Unrealized gains/(losses) included in OCI, assets |  | 5 | (1)
Foreign exchange recognized in OCI or earnings, assets |  | 0 | 1
Purchases, assets |  | 146 | 112
Issuances, assets |  | 0 | 0
Settlements, assets |  | (99) | (68)
Sales, assets |  | 0 | (16)
Transfers into level 3, assets | [1] | 5 | 0
Transfers out of level 3, assets | [1] | (11) | (11)
Ending balance, fair value assets |  | 1,850 | 2,122
Change in unrealized gains/(losses) for the period included in earnings for assets still held, assets |  | (18) | 12
Beginning balance, fair value liabilities |  | 1,531 | 1,200
Realized gains/(losses), liabilities |  | 14 | 9
Unrealized gains/(losses included in earnings, liabilities |  | (10) | (27)
Unrealized gains/(losses) included in OCI, liabilities |  | 0 | 0
Foreign exchange recognized in OCI or earnings, liabilities |  | 7 | (22)
Purchases, liabilities |  | 9 | 695
Issuances, liabilities |  | 0 | 0
Settlements, liabilities |  | (92) | (60)
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 |  | 1,459 | 1,795
Change in unrealized gains/(losses) for the period included in earnings for liabilities still held, liabilities |  | 0 | (49)
Residential Prime Financing Receivable [Member] | Variable Interest Entity Primary Beneficiary [Member] |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |
Beginning balance, fair value assets |  | 1,185 | 1,431
Unrealized gains/(losses) included in earnings, assets |  | (14) | (3)
Settlements, assets |  | (56) | (56)
Ending balance, fair value assets |  | 1,115 | 1,372
Change in unrealized gains/(losses) for the period included in earnings for assets still held, assets |  | (14) | (3)
Other Loans Receivable [Member] | Variable Interest Entity Primary Beneficiary [Member] |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |
Beginning balance, fair value assets |  | 107 |
Purchases, assets |  | 146 | 108
Ending balance, fair value assets |  | 253 | 108
Loan Repurchase Commitments [Member] | Variable Interest Entity Primary Beneficiary [Member] |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |
Beginning balance, fair value assets |  | 396 | 379
Unrealized gains/(losses) included in earnings, assets |  | 3 | 6
Ending balance, fair value assets |  | 399 | 385
Change in unrealized gains/(losses) for the period included in earnings for assets still held, assets |  | 3 | 6
State and municipal bonds [Member] |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |
Beginning balance, fair value assets |  | 41 | 8
Settlements, assets |  | (38) |
Transfers out of level 3, assets |  |  | (2)
Ending balance, fair value assets |  | 3 | 6
Foreign Government Debt [Member] |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |
Beginning balance, fair value assets |  | 2 | 6
Ending balance, fair value assets |  | 2 | 6
Corporate Obligations [Member] |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |
Beginning balance, fair value assets |  | 7 | 10
Transfers out of level 3, assets | [1] | (6) |
Ending balance, fair value assets |  | 1 | 10
Corporate Obligations [Member] | Variable Interest Entity Primary Beneficiary [Member] |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |
Beginning balance, fair value assets |  | 11 | 55
Unrealized gains/(losses) included in earnings, assets |  | (5) |
Settlements, assets |  |  | (2)
Transfers out of level 3, assets |  | (5) |
Ending balance, fair value assets |  | 1 | 53
Residential Mortgage Backed Non Agency [Member] | Variable Interest Entity Primary Beneficiary [Member] |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |
Beginning balance, fair value assets |  |  | 3
Unrealized gains/(losses) included in earnings, assets |  |  | 1
Settlements, assets |  |  | (1)
Ending balance, fair value assets |  |  | 3
Change in unrealized gains/(losses) for the period included in earnings for assets still held, assets |  |  | 1
Commercial Mortgage Backed Securities [Member] |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |
Beginning balance, fair value assets |  |  | 2
Transfers out of level 3, assets |  |  | (1)
Ending balance, fair value assets |  |  | 1
Commercial Mortgage Backed Securities [Member] | Variable Interest Entity Primary Beneficiary [Member] |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |
Transfers into level 3, assets |  | 2 |
Ending balance, fair value assets |  | 2 |
Collateralized Debt Obligations [Member] |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |
Beginning balance, fair value assets |  | 29 | 87
Settlements, assets |  | (3) | (5)
Sales, assets |  |  | (8)
Ending balance, fair value assets |  | 26 | 74
Collateralized Debt Obligations [Member] | Variable Interest Entity Primary Beneficiary [Member] |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |
Beginning balance, fair value assets |  | 1 | 5
Unrealized gains/(losses) included in earnings, assets |  |  | (1)
Ending balance, fair value assets |  | 1 | 4
Other Asset Backed [Member] |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |
Beginning balance, fair value assets |  | 38 | 85
Realized gains/(losses), assets |  | (1) | (2)
Unrealized gains/(losses) included in earnings, assets |  | (1) |
Unrealized gains/(losses) included in OCI, assets |  | 5 | (1)
Purchases, assets |  |  | 4
Settlements, assets |  | (2) | (2)
Sales, assets |  |  | (8)
Transfers out of level 3, assets | [1] |  | (2)
Ending balance, fair value assets |  | 39 | 74
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 |  | 6 | 26
Unrealized gains/(losses) included in earnings, assets |  | (6) | 3
Settlements, assets |  |  | (2)
Transfers into level 3, assets |  | 3 |
Transfers out of level 3, assets |  |  | (6)
Ending balance, fair value assets |  | 3 | 21
Change in unrealized gains/(losses) for the period included in earnings for assets still held, assets |  |  | 3
Medium Term Notes [Member] |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |
Beginning balance, fair value liabilities |  | 161 | 197
Unrealized gains/(losses included in earnings, liabilities |  | (3) | 5
Foreign exchange recognized in OCI or earnings, liabilities |  | 7 | (22)
Ending balance, fair value liabilities |  | 165 | 180
Change in unrealized gains/(losses) for the period included in earnings for liabilities still held, liabilities |  | 5 | (17)
Credit Derivatives [Member] |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |
Beginning balance, fair value liabilities |  | 85 | 244
Realized gains/(losses), liabilities |  | 14 | 9
Unrealized gains/(losses included in earnings, liabilities |  | 14 | (37)
Settlements, liabilities |  | (14) | (9)
Ending balance, fair value liabilities |  | 99 | 207
Change in unrealized gains/(losses) for the period included in earnings for liabilities still held, liabilities |  | 16 | (37)
Other Derivative Liabilities [Member] |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |
Beginning balance, fair value liabilities |  | 18 | 24
Unrealized gains/(losses included in earnings, liabilities |  | 1 | (3)
Ending balance, fair value liabilities |  | 19 | 21
Change in unrealized gains/(losses) for the period included in earnings for liabilities still held, liabilities |  | 1 | (3)
Variable Interest Entity Notes [Member] | Variable Interest Entity Primary Beneficiary [Member] |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |
Beginning balance, fair value liabilities |  | 1,267 | 735
Unrealized gains/(losses included in earnings, liabilities |  | (22) | 8
Purchases, liabilities |  | 9 | 695
Settlements, liabilities |  | (78) | (51)
Ending balance, fair value liabilities |  | 1,176 | 1,387
Change in unrealized gains/(losses) for the period included in earnings for liabilities still held, liabilities |  | (22) | 8
Currency Derivatives [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) | 4
Foreign exchange recognized in OCI or earnings, assets |  |  | 1
Ending balance, fair value assets |  | 5 | 5
Change in unrealized gains/(losses) for the period included in earnings for assets still held, assets |  | $ (6) | $ 5
[1] | (1) - Transferred in and out at the end of the period.

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