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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 | 9 Months Ended
--- | --- | ---
Sep. 30, 2018 | Sep. 30, 2017 | Sep. 30, 2018 | Sep. 30, 2017
Accounts Notes And Loans Receivable [Line Items] |  |  |  |
Beginning balance, fair value assets | $ 1,138 | $ 2,122 | $ 2,140 | $ 1,552
Realized gains/(losses), assets | 0 | 0 | 0 | 0
Unrealized gains/(losses) included in earnings, assets | 23 | 8 | 43 | 65
Unrealized gains/(losses) included in OCI, assets | 0 | 0 | 0 | 2
Foreign exchange recognized in OCI or earnings, assets | (2) | 1 | (2) | (4)
Purchases, assets | 0 | 17 | 5 | 736
Issuances, assets | 0 | 0 | 0 | 0
Settlements, assets | (24) | (64) | (115) | (268)
Sales, assets | (251) | (3) | (1,178) | (3)
Transfers into level 3, assets | 7 | 0 | 13 | 18
Transfers out of level 3, assets | (2) | (7) | (17) | (24)
Ending balance, fair value assets | 889 | 2,074 | 889 | 2,074
Change in unrealized gains/(losses) for the period included in earnings for assets still held, assets | 22 | 9 | 27 | 61
Beginning balance, fair value liabilities | 578 | 698 | 595 | 661
Realized gains/(losses), liabilities | 11 | 7 | 66 | 41
Unrealized gains/(losses included in earnings, liabilities | 1 | (2) | (44) | 98
Unrealized gains/(losses) included in OCI, liabilities | 0 | 0 | 41 | 0
Foreign exchange recognized in OCI or earnings, liabilities | 4 | 5 | (4) | 13
Purchases, liabilities | 0 | 6 | 0 | 6
Issuances, liabilities | 1 | 0 | 7 | 0
Settlements, liabilities | (51) | (21) | (117) | (126)
Sales, liabilities | 0 | (51) | 0 | (51)
Transfers into Level 3, liabilities | 0 | 0 | 0 | 0
Transfers out of Level 3, liabilities | 0 | 0 | 0 | 0
Ending balance, fair value liabilities | 544 | 642 | 544 | 642
Change in unrealized gains/(losses) for the period included in earnings for liabilities still held, liabilities | 5 | 3 | (48) | 113
Residential Prime Financing Receivable [Member] | Variable Interest Entity Primary Beneficiary [Member] |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |
Beginning balance, fair value assets | 683 | 815 | 759 | 916
Unrealized gains/(losses) included in earnings, assets | 20 | 2 | 26 | 29
Settlements, assets | (24) | (58) | (106) | (186)
Sales, assets | (251) |  | (251) |
Ending balance, fair value assets | 428 | 759 | 428 | 759
Change in unrealized gains/(losses) for the period included in earnings for assets still held, assets | 21 | 2 | 23 | 29
Corporate Loans Receivable [Member] | Variable Interest Entity Primary Beneficiary [Member] |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |
Beginning balance, fair value assets |  | 875 | 920 | 150
Unrealized gains/(losses) included in earnings, assets |  | 4 | 11 | 36
Purchases, assets |  |  |  | 719
Settlements, assets |  | (6) | (6) | (32)
Sales, assets |  |  | (925) |
Ending balance, fair value assets |  | 873 |  | 873
Change in unrealized gains/(losses) for the period included in earnings for assets still held, assets |  | 4 |  | 36
Loan Repurchase Commitments [Member] | Variable Interest Entity Primary Beneficiary [Member] |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |
Beginning balance, fair value assets | 415 | 407 | 407 | 404
Unrealized gains/(losses) included in earnings, assets |  | (1) | 8 | 2
Ending balance, fair value assets | 415 | 406 | 415 | 406
Change in unrealized gains/(losses) for the period included in earnings for assets still held, assets |  | (1) | 8 | 2
State and municipal bonds [Member] |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |
Transfers into level 3, assets |  |  |  | 1
Transfers out of level 3, 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] |  |  |  |
Beginning balance, fair value assets | 5 |  |  |
Settlements, assets |  |  | (1) | (2)
Transfers into level 3, assets |  |  | 6 | 6
Transfers out of level 3, assets |  |  |  | (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 | 7
Transfers out of level 3, assets |  | (7) | (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 |  | 3 | 6 |
Sales, assets |  | (3) |  | (3)
Transfers into level 3, assets |  |  |  | 3
Transfers out of level 3, assets |  |  | (6) |
Collateralized Debt Obligations [Member] |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |
Beginning balance, fair value assets |  |  |  | 15
Settlements, assets |  |  |  | (7)
Transfers out of level 3, assets |  |  |  | (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 | 6 | 5 | 5 | 44
Unrealized gains/(losses) included in OCI, assets |  |  |  | 2
Purchases, assets |  |  | 5 |
Settlements, assets |  |  | (2) | (41)
Sales, assets |  |  | (2) |
Transfers out of level 3, assets | (2) |  | (2) |
Ending balance, fair value assets | 4 | 5 | 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 |  |  |  | (2)
Medium Term Notes [Member] |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |
Beginning balance, fair value liabilities | 149 | 123 | 115 | 101
Realized gains/(losses), liabilities | (5) |  | (5) |
Unrealized gains/(losses included in earnings, liabilities | (1) | (1) | (1) | 13
Unrealized gains/(losses) included in OCI, liabilities | 11 |  | 51 |
Foreign exchange recognized in OCI or earnings, liabilities | (1) | 5 | (7) | 13
Settlements, liabilities | (30) |  | (30) |
Ending balance, fair value liabilities | 123 | 127 | 123 | 127
Change in unrealized gains/(losses) for the period included in earnings for liabilities still held, liabilities | (2) | 4 | (8) | 26
Credit Derivatives [Member] |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |
Beginning balance, fair value liabilities | 31 | 80 | 63 | 64
Realized gains/(losses), liabilities | 6 | 7 | 49 | 41
Unrealized gains/(losses included in earnings, liabilities | (4) | (6) | (36) | 10
Settlements, liabilities | (6) | (7) | (49) | (41)
Ending balance, fair value liabilities | 27 | 74 | 27 | 74
Change in unrealized gains/(losses) for the period included in earnings for liabilities still held, liabilities | (4) | (6) | (36) | 12
Other Derivative Liabilities [Member] |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |
Beginning balance, fair value liabilities | 4 | 4 | 4 | 20
Unrealized gains/(losses included in earnings, liabilities | 3 |  | 3 | 18
Settlements, liabilities |  |  |  | (34)
Ending balance, fair value liabilities | 7 | 4 | 7 | 4
Change in unrealized gains/(losses) for the period included in earnings for liabilities still held, liabilities | 3 |  | 3 | 18
Variable Interest Entity Notes [Member] | Variable Interest Entity Primary Beneficiary [Member] |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |
Beginning balance, fair value liabilities | 389 | 491 | 406 | 476
Realized gains/(losses), liabilities | 10 |  | 22 |
Unrealized gains/(losses included in earnings, liabilities | 3 | 4 | (12) | 56
Unrealized gains/(losses) included in OCI, liabilities | (11) |  | (10) |
Foreign exchange recognized in OCI or earnings, liabilities | 5 |  | 3 |
Issuances, liabilities | 1 |  | 7 |
Settlements, liabilities | (15) | (14) | (34) | (51)
Sales, liabilities |  | (51) |  | (51)
Ending balance, fair value liabilities | 382 | 430 | 382 | 430
Change in unrealized gains/(losses) for the period included in earnings for liabilities still held, liabilities | 8 | 4 | (9) | 56
Currency Derivatives [Member] | Variable Interest Entity Primary Beneficiary [Member] |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |
Beginning balance, fair value assets | 14 | 9 | 19 | 19
Unrealized gains/(losses) included in earnings, assets | 2 | 3 | (3) | (2)
Foreign exchange recognized in OCI or earnings, assets | (2) | 1 | (2) | (4)
Ending balance, fair value assets | 14 | 13 | 14 | 13
Change in unrealized gains/(losses) for the period included in earnings for assets still held, assets |  | 4 | (5) | (6)
Other Assets [Member] | Variable Interest Entity Primary Beneficiary [Member] |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |
Beginning balance, fair value assets | 14 |  | 14 |
Unrealized gains/(losses) included in earnings, assets | 1 |  | 1 |
Purchases, assets |  | 17 |  | 17
Ending balance, fair value assets | 15 | 17 | 15 | 17
Change in unrealized gains/(losses) for the period included in earnings for assets still held, assets | 1 |  | 1 |
Other Payable [Member] |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |
Beginning balance, fair value liabilities | 5 |  | 7 |
Unrealized gains/(losses included in earnings, liabilities |  | 1 | 2 | 1
Purchases, liabilities |  | 6 |  | 6
Settlements, liabilities |  |  | (4) |
Ending balance, fair value liabilities | $ 5 | 7 | 5 | 7
Change in unrealized gains/(losses) for the period included in earnings for liabilities still held, liabilities |  | $ 1 | $ 2 | $ 1

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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 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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