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Derivative Financial Instruments - Mark-to-Market Impact of Derivatives on Statements of Income (Detail) - USD ($) $ in Millions | 3 Months Ended | 6 Months Ended
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Jun. 30, 2021 | Jun. 30, 2020 | Jun. 30, 2021 | Jun. 30, 2020
Derivative Instruments, Gain (Loss) [Line Items] |  |  |  |
Mark-to-market gains (losses) recognized | $ (10) | $ (30) | $ 26 | $ (253)
Interest Expense and Derivative Instruments Hedging Activities [Member] |  |  |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |  |  |
Mark-to-market gains (losses) recognized | 6 | (36) | 87 | (268)
Designated as Hedging Instrument [Member] | Fair Value [Member] |  |  |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |  |  |
Mark-to-market gains (losses) recognized | 16 | (6) | 61 | (15)
Designated as Hedging Instrument [Member] | Fair Value [Member] | Interest Rate Swaps [Member] |  |  |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |  |  |
Gains (losses) recognized in net income on derivatives | 22 | 15 | (175) | 424
Gains (losses) recognized in net income on hedged items | (21) | (27) | 191 | (455)
Net fair value hedge ineffectiveness gains (losses) | 1 | (12) | 16 | (31)
Designated as Hedging Instrument [Member] | Fair Value [Member] | Cross-Currency Interest Rate Swaps [Member] |  |  |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |  |  |
Gains (losses) recognized in net income on derivatives | 117 | 60 | 186 | (31)
Gains (losses) recognized in net income on hedged items | (102) | (54) | (141) | 47
Net fair value hedge ineffectiveness gains (losses) | 15 | 6 | 45 | 16
Trading [Member] |  |  |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |  |  |
Mark-to-market gains (losses) recognized | (10) | (30) | 26 | (253)
Trading [Member] | Interest Rate Swaps [Member] |  |  |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |  |  |
Mark-to-market gains (losses) recognized | (7) | (6) | 15 | (47)
Trading [Member] | Floor Income Contracts [Member] |  |  |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |  |  |
Mark-to-market gains (losses) recognized | $ (3) | $ (24) | $ 11 | $ (206)

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- Definition Amount of the increase (decrease) in fair value of the hedged item in a fair value hedge recognized in the income statement. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 25 -Section 50 -Paragraph 1 -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=121577467&loc=d3e76258-113986 + Details
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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
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- Definition The portion of gains and losses (net) on derivative instruments designated and qualifying as hedging instruments representing (a) the amount of the hedge ineffectiveness and (b) the amount, if any, excluded from the assessment of hedge effectiveness. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 4C -Subparagraph (d) -URI http://asc.fasb.org/extlink&oid=121590274&loc=SL5624171-113959 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 25 -Section 50 -Paragraph 1 -Subparagraph (a)(1),(2) -URI http://asc.fasb.org/extlink&oid=121577467&loc=d3e76258-113986 + Details
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- Definition Amount of gain (loss) from the ineffectiveness of the hedge. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 25 -Section 50 -Paragraph 1 -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=121577467&loc=d3e76258-113986 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 4C -Subparagraph (d)(1) -URI http://asc.fasb.org/extlink&oid=121590274&loc=SL5624171-113959 + Details
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- Definition Aggregate net gain (loss) on all derivative instruments recognized in earnings during the period, before tax effects. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 4A -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=121590274&loc=SL5618551-113959 + Details
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