Derivative Financial Instruments - Mark-to-Market Impact of Derivatives on Statements of Income (Detail) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
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)

Amount of the increase (decrease) in fair value of the hedged item in a fair value hedge recognized in the income statement.

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+ References

No definition available.

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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
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-Topic 815
-SubTopic 10
-Section 50
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Amount of gain (loss) from the ineffectiveness of the hedge.

+ References

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Aggregate net gain (loss) on all derivative instruments recognized in earnings during the period, before tax effects.

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