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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 | 6 Months Ended
--- | --- | ---
Jun. 30, 2018 | Jun. 30, 2017 | Jun. 30, 2018 | Jun. 30, 2017
Accounts Notes And Loans Receivable [Line Items] |  |  |  |
Beginning balance, fair value assets | $ 2,117 | $ 2,165 | $ 2,140 | $ 1,552
Realized gains/(losses), assets | 0 | 0 | 0 | 0
Unrealized gains/(losses) included in earnings, assets | (8) | 56 | 20 | 57
Unrealized gains/(losses) included in OCI, assets | 0 | 0 | 0 | 2
Foreign exchange recognized in OCI or earnings, assets | 3 | (2) | 0 | (5)
Purchases, assets | 2 | 0 | 5 | 719
Issuances, assets | 0 | 0 | 0 | 0
Settlements, assets | (41) | (93) | (90) | (205)
Sales, assets | (925) | 0 | (928) | 0
Transfers into level 3, assets | 3 | 10 | 6 | 18
Transfers out of level 3, assets | (13) | (14) | (15) | (16)
Ending balance, fair value assets | 1,138 | 2,122 | 1,138 | 2,122
Change in unrealized gains/(losses) for the period included in earnings for assets still held, assets | (5) | 54 | 9 | 52
Beginning balance, fair value liabilities | 604 | 701 | 595 | 661
Realized gains/(losses), liabilities | 29 | 3 | 56 | 34
Unrealized gains/(losses included in earnings, liabilities | (31) | 42 | (46) | 99
Unrealized gains/(losses) included in OCI, liabilities | 24 | 0 | 41 | 0
Foreign exchange recognized in OCI or earnings, liabilities | (18) | 7 | (8) | 9
Purchases, liabilities | 0 | 0 | 0 | 0
Issuances, liabilities | 1 | 0 | 6 | 0
Settlements, liabilities | (31) | (55) | (66) | (105)
Sales, liabilities | 0 | 0 | 0 | 0
Transfers into Level 3, liabilities | 0 | 0 | 0 | 0
Transfers out of Level 3, liabilities | 0 | 0 | 0 | 0
Ending balance, fair value liabilities | 578 | 698 | 578 | 698
Change in unrealized gains/(losses) for the period included in earnings for liabilities still held, liabilities | (49) | 49 | (54) | 108
Residential Prime Financing Receivable [Member] | Variable Interest Entity Primary Beneficiary [Member] |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |
Beginning balance, fair value assets | 737 | 844 | 759 | 916
Unrealized gains/(losses) included in earnings, assets | (14) | 31 | 6 | 27
Settlements, assets | (40) | (60) | (82) | (128)
Ending balance, fair value assets | 683 | 815 | 683 | 815
Change in unrealized gains/(losses) for the period included in earnings for assets still held, assets | (14) | 31 | 6 | 27
Corporate Loans Receivable [Member] | Variable Interest Entity Primary Beneficiary [Member] |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |
Beginning balance, fair value assets | 925 | 872 | 920 | 150
Unrealized gains/(losses) included in earnings, assets |  | 29 | 11 | 32
Purchases, assets |  |  |  | 719
Settlements, assets |  | (26) | (6) | (26)
Sales, assets | (925) |  | (925) |
Ending balance, fair value assets |  | 875 |  | 875
Change in unrealized gains/(losses) for the period included in earnings for assets still held, assets |  | 29 |  | 32
Loan Repurchase Commitments [Member] | Variable Interest Entity Primary Beneficiary [Member] |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |
Beginning balance, fair value assets | 407 | 409 | 407 | 404
Unrealized gains/(losses) included in earnings, assets | 8 | (2) | 8 | 3
Ending balance, fair value assets | 415 | 407 | 415 | 407
Change in unrealized gains/(losses) for the period included in earnings for assets still held, assets | 8 | (2) | 8 | 3
State and municipal bonds [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) |  | (1)
Corporate Obligations [Member] |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |
Beginning balance, fair value assets |  |  | 2 | 2
Settlements, assets |  |  |  | (1)
Transfers out of level 3, assets |  |  | (2) | (1)
Corporate Obligations [Member] | Variable Interest Entity Primary Beneficiary [Member] |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |
Beginning balance, fair value assets | 3 | 6 |  |
Settlements, assets | (1) | (2) | (1) | (2)
Transfers into level 3, assets | 3 |  | 6 | 6
Transfers out of level 3, assets |  | (4) |  | (4)
Ending balance, fair value assets | 5 |  | 5 |
Commercial Mortgage Backed Securities [Member] |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |
Beginning balance, fair value assets | 7 |  | 7 |
Transfers into level 3, assets |  | 7 |  | 7
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 |  | 6 |
Transfers into level 3, assets |  | 3 |  | 3
Transfers out of level 3, assets | (6) |  | (6) |
Ending balance, fair value assets |  | 3 |  | 3
Collateralized Debt Obligations [Member] |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |
Beginning balance, fair value assets |  | 13 |  | 15
Settlements, assets |  | (5) |  | (7)
Transfers out of level 3, assets |  | (8) |  | (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 | 1 | 1
Ending balance, fair value assets | 1 | 1 | 1 | 1
Other Asset Backed [Member] |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |
Beginning balance, fair value assets | 4 | 5 | 5 | 44
Unrealized gains/(losses) included in OCI, assets |  |  |  | 2
Purchases, assets | 2 |  | 5 |
Settlements, assets |  |  | (1) | (41)
Sales, assets |  |  | (3) |
Ending balance, fair value assets | 6 | 5 | 6 | 5
Other Asset Backed [Member] | Variable Interest Entity Primary Beneficiary [Member] |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |
Beginning balance, fair value assets |  | 1 |  | 1
Transfers into level 3, assets |  |  |  | 1
Transfers out of level 3, assets |  | (1) |  | (2)
Medium Term Notes [Member] |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |
Beginning balance, fair value liabilities | 146 | 104 | 115 | 101
Unrealized gains/(losses included in earnings, liabilities | (1) | 12 |  | 13
Unrealized gains/(losses) included in OCI, liabilities | 15 |  | 40 |
Foreign exchange recognized in OCI or earnings, liabilities | (11) | 7 | (6) | 9
Ending balance, fair value liabilities | 149 | 123 | 149 | 123
Change in unrealized gains/(losses) for the period included in earnings for liabilities still held, liabilities | (12) | 19 | (6) | 22
Credit Derivatives [Member] |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |
Beginning balance, fair value liabilities | 49 | 86 | 63 | 64
Realized gains/(losses), liabilities | 25 | 3 | 44 | 34
Unrealized gains/(losses included in earnings, liabilities | (18) | (6) | (32) | 16
Settlements, liabilities | (25) | (3) | (44) | (34)
Ending balance, fair value liabilities | 31 | 80 | 31 | 80
Change in unrealized gains/(losses) for the period included in earnings for liabilities still held, liabilities | (18) | (6) | (32) | 16
Other Derivative Liabilities [Member] |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |
Beginning balance, fair value liabilities | 4 | 20 | 4 | 20
Unrealized gains/(losses included in earnings, liabilities |  | 18 |  | 18
Settlements, liabilities |  | (34) |  | (34)
Ending balance, fair value liabilities | 4 | 4 | 4 | 4
Change in unrealized gains/(losses) for the period included in earnings for liabilities still held, liabilities |  | 18 |  | 18
Variable Interest Entity Notes [Member] | Variable Interest Entity Primary Beneficiary [Member] |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |
Beginning balance, fair value liabilities | 400 | 491 | 406 | 476
Realized gains/(losses), liabilities | 4 |  | 12 |
Unrealized gains/(losses included in earnings, liabilities | (12) | 18 | (16) | 52
Unrealized gains/(losses) included in OCI, liabilities | 9 |  | 1 |
Foreign exchange recognized in OCI or earnings, liabilities | (7) |  | (2) |
Issuances, liabilities | 1 |  | 6 |
Settlements, liabilities | (6) | (18) | (18) | (37)
Ending balance, fair value liabilities | 389 | 491 | 389 | 491
Change in unrealized gains/(losses) for the period included in earnings for liabilities still held, liabilities | (19) | 18 | (18) | 52
Currency Derivatives [Member] | Variable Interest Entity Primary Beneficiary [Member] |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |
Beginning balance, fair value assets | 13 | 13 | 19 | 19
Unrealized gains/(losses) included in earnings, assets | (2) | (2) | (5) | (5)
Foreign exchange recognized in OCI or earnings, assets | 3 | (2) |  | (5)
Ending balance, fair value assets | 14 | 9 | 14 | 9
Change in unrealized gains/(losses) for the period included in earnings for assets still held, assets | 1 | $ (4) | (5) | $ (10)
Other Assets [Member] | Variable Interest Entity Primary Beneficiary [Member] |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |
Beginning balance, fair value assets | 14 |  | 14 |
Ending balance, fair value assets | 14 |  | 14 |
Other Payable [Member] |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |
Beginning balance, fair value liabilities | 5 |  | 7 |
Unrealized gains/(losses included in earnings, liabilities |  |  | 2 |
Settlements, liabilities |  |  | (4) |
Ending balance, fair value liabilities | $ 5 |  | 5 |
Change in unrealized gains/(losses) for the period included in earnings for liabilities still held, liabilities |  |  | $ 2 |

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- Definition Amount of transfer of financial instrument classified as an asset into level 3 of the fair value hierarchy. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(3) -URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19207-110258 + Details
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- Definition Amount of transfers of financial instrument classified as an asset out of level 3 of the fair value hierarchy. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(3) -URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19207-110258 + Details
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- Definition Amount of purchases of financial instrument classified as a liability measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(2) -URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19207-110258 + Details
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- Definition Amount of sales of financial instrument classified as a liability measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(2) -URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19207-110258 + Details
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- Definition Fair value of financial instrument classified as a liability measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19207-110258 + Details
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