Concentration risk threshold percentage.

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- Definition

Loans In Repayment And Percentage Of Each Status [Abstract]

+ References

No definition available.

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- Definition

Amount of allowance for credit loss on financing receivable. Excludes allowance for financing receivable covered under loss sharing agreement.

+ References

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- Definition

Amortized cost, before allowance for credit loss, fee, and loan in process, of financing receivable. Excludes financing receivable covered under loss sharing agreement and net investment in lease.

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- Definition

Percentage of financing receivable balance that is past due.

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- Definition

Amortized cost, before allowance for credit loss, of financing receivable. Excludes financing receivable covered under loss sharing agreement and net investment in lease.

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Amortized cost, after allowance for credit loss, of financing receivable. Excludes financing receivable covered under loss sharing agreement and net investment in lease.

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Allowance for Loan Losses - Age Analysis of Past Due Loans Delinquencies (Detail) - USD ($) $ in Millions	6 Months Ended		12 Months Ended
	Jun. 30, 2025	Jun. 30, 2024	Dec. 31, 2024	Mar. 31, 2025	Mar. 31, 2024	Dec. 31, 2023
Loans in repayment and percentage of each status:
Loan allowance for losses	$ (530)	$ (687)	$ (621)	$ (579)	$ (744)	$ (832)
FFELP Loans [Member]
Loans in repayment and percentage of each status:
Total Loans, gross	29,800	33,134
Loan allowance for losses	(182)	(194)	(180)	(182)	(206)	(215)
Loans, net	29,618		30,852
Credit Concentration Risk [Member] \| Accounts Receivable [Member] \| FFELP Loans [Member]
Loans in repayment and percentage of each status:
Total Loans, gross	29,800	33,134	31,032
Loan allowance for losses	(182)	(194)	(180)
Loans, net	$ 29,618	$ 32,940	$ 30,852
Dimensions of concentration risk	100.00%	100.00%	100.00%
Credit Concentration Risk [Member] \| Financing Receivables, Current [Member] \| Accounts Receivable [Member] \| FFELP Loans [Member]
Loans in repayment and percentage of each status:
Dimensions of concentration risk	81.00%	86.50%	81.40%
Credit Concentration Risk [Member] \| Financing Receivables, 31 to 60 Days Past Due [Member] \| Accounts Receivable [Member] \| FFELP Loans [Member]
Loans in repayment and percentage of each status:
Loans delinquent, percentage	5.40%	3.90%	5.80%
Credit Concentration Risk [Member] \| Financing Receivables, 61 to 90 Days Past Due [Member] \| Accounts Receivable [Member] \| FFELP Loans [Member]
Loans in repayment and percentage of each status:
Loans delinquent, percentage	3.50%	2.60%	4.10%
Credit Concentration Risk [Member] \| Financing Receivables, 90 Days Past Due [Member] \| Accounts Receivable [Member] \| FFELP Loans [Member]
Loans in repayment and percentage of each status:
Loans delinquent, percentage	10.10%	7.00%	8.70%
Credit Concentration Risk [Member] \| Financing Receivables, Loans In Repayment [Member] \| Accounts Receivable [Member] \| FFELP Loans [Member]
Loans in repayment and percentage of each status:
Dimensions of concentration risk	83.40%	79.70%	81.90%
Credit Concentration Risk [Member] \| Financing Receivables, Delinquent Loans in Repayment [Member] \| Accounts Receivable [Member] \| FFELP Loans [Member]
Loans in repayment and percentage of each status:
Dimensions of concentration risk	19.00%	13.50%	18.60%
Credit Concentration Risk [Member] \| Financing Receivables, Forbearance, Loans In Repayment [Member] \| Accounts Receivable [Member] \| FFELP Loans [Member]
Loans in repayment and percentage of each status:
Dimensions of concentration risk	12.80%	16.80%	14.70%
School/Grace/Deferment [Member] \| Credit Concentration Risk [Member] \| Accounts Receivable [Member] \| FFELP Loans [Member]
Loans in repayment and percentage of each status:
Total Loans, gross	$ 1,280	$ 1,403	$ 1,262
Forbearance [Member] \| Credit Concentration Risk [Member] \| Accounts Receivable [Member] \| FFELP Loans [Member]
Loans in repayment and percentage of each status:
Total Loans, gross	3,653	5,320	4,365
Repayment [Member] \| Credit Concentration Risk [Member] \| Accounts Receivable [Member] \| FFELP Loans [Member]
Loans in repayment and percentage of each status:
Total Loans, gross	24,867	26,411	25,405
Repayment [Member] \| Credit Concentration Risk [Member] \| Financing Asset, Not Past Due [Member] \| Accounts Receivable [Member] \| FFELP Loans [Member]
Loans in repayment and percentage of each status:
Total Loans, gross	20,145	22,833	20,675
Repayment [Member] \| Credit Concentration Risk [Member] \| Financial Asset, 31 to 60 Days Past Due [Member] \| Accounts Receivable [Member] \| FFELP Loans [Member]
Loans in repayment and percentage of each status:
Total Loans, gross	1,333	1,041	1,479
Repayment [Member] \| Credit Concentration Risk [Member] \| Financial Asset, 61 to 90 Days Past Due [Member] \| Accounts Receivable [Member] \| FFELP Loans [Member]
Loans in repayment and percentage of each status:
Total Loans, gross	863	680	1,043
Repayment [Member] \| Credit Concentration Risk [Member] \| Financial Asset, 90 Days Past Due [Member] \| Accounts Receivable [Member] \| FFELP Loans [Member]
Loans in repayment and percentage of each status:
Total Loans, gross	2,526	1,857	2,208
Private Education Loans [Member]
Loans in repayment and percentage of each status:
Total Loans, gross	15,878	16,731
Loan allowance for losses	(348)	(493)	(441)	$ (397)	$ (538)	$ (617)
Loans, net	15,530	16,238	15,716
Private Education Loans [Member] \| Credit Concentration Risk [Member] \| Accounts Receivable [Member]
Loans in repayment and percentage of each status:
Total Loans, gross	15,878	16,731	16,157
Loan allowance for losses	(348)	(493)	(441)
Loans, net	$ 15,530	$ 16,238	$ 15,716
Dimensions of concentration risk	100.00%	100.00%	100.00%
Private Education Loans [Member] \| Credit Concentration Risk [Member] \| Financing Receivables, Current [Member] \| Accounts Receivable [Member]
Loans in repayment and percentage of each status:
Dimensions of concentration risk	93.60%	94.80%	93.90%
Private Education Loans [Member] \| Credit Concentration Risk [Member] \| Financing Receivables, 31 to 60 Days Past Due [Member] \| Accounts Receivable [Member]
Loans in repayment and percentage of each status:
Loans delinquent, percentage	2.20%	1.90%	2.10%
Private Education Loans [Member] \| Credit Concentration Risk [Member] \| Financing Receivables, 61 to 90 Days Past Due [Member] \| Accounts Receivable [Member]
Loans in repayment and percentage of each status:
Loans delinquent, percentage	1.20%	1.10%	1.30%
Private Education Loans [Member] \| Credit Concentration Risk [Member] \| Financing Receivables, 90 Days Past Due [Member] \| Accounts Receivable [Member]
Loans in repayment and percentage of each status:
Loans delinquent, percentage	3.00%	2.20%	2.70%
Private Education Loans [Member] \| Credit Concentration Risk [Member] \| Financing Receivables, Loans In Repayment [Member] \| Accounts Receivable [Member]
Loans in repayment and percentage of each status:
Dimensions of concentration risk	96.20%	96.20%	95.10%
Private Education Loans [Member] \| Credit Concentration Risk [Member] \| Financing Receivables, Delinquent Loans in Repayment [Member] \| Accounts Receivable [Member]
Loans in repayment and percentage of each status:
Dimensions of concentration risk	6.40%	5.20%	6.10%
Private Education Loans [Member] \| Credit Concentration Risk [Member] \| Financing Receivables, Forbearance, Loans In Repayment [Member] \| Accounts Receivable [Member]
Loans in repayment and percentage of each status:
Dimensions of concentration risk	1.60%	1.80%	2.70%
Private Education Loans [Member] \| School/Grace/Deferment [Member] \| Credit Concentration Risk [Member] \| Accounts Receivable [Member]
Loans in repayment and percentage of each status:
Total Loans, gross	$ 361	$ 350	$ 372
Private Education Loans [Member] \| Forbearance [Member] \| Credit Concentration Risk [Member] \| Accounts Receivable [Member]
Loans in repayment and percentage of each status:
Total Loans, gross	250	294	422
Private Education Loans [Member] \| Repayment [Member] \| Credit Concentration Risk [Member] \| Accounts Receivable [Member]
Loans in repayment and percentage of each status:
Total Loans, gross	15,267	16,087	15,363
Private Education Loans [Member] \| Repayment [Member] \| Credit Concentration Risk [Member] \| Financing Asset, Not Past Due [Member] \| Accounts Receivable [Member]
Loans in repayment and percentage of each status:
Total Loans, gross	14,296	15,250	14,419
Private Education Loans [Member] \| Repayment [Member] \| Credit Concentration Risk [Member] \| Financial Asset, 31 to 60 Days Past Due [Member] \| Accounts Receivable [Member]
Loans in repayment and percentage of each status:
Total Loans, gross	335	311	319
Private Education Loans [Member] \| Repayment [Member] \| Credit Concentration Risk [Member] \| Financial Asset, 61 to 90 Days Past Due [Member] \| Accounts Receivable [Member]
Loans in repayment and percentage of each status:
Total Loans, gross	177	175	206
Private Education Loans [Member] \| Repayment [Member] \| Credit Concentration Risk [Member] \| Financial Asset, 90 Days Past Due [Member] \| Accounts Receivable [Member]
Loans in repayment and percentage of each status:
Total Loans, gross	$ 459	$ 351	$ 419