Borrowings - Company's Borrowings (Detail) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Debt Instrument [Line Items]
Short-term borrowings, Carrying Value	$ 4,226	$ 5,870
Short-term Weighted Average Interest Rate	6.67%	5.78%
Long-term borrowings, Carrying Value	$ 53,402	$ 61,026
Long-term Weighted Average Interest Rate	5.62%	4.70%
Total	$ 57,628	$ 66,896
FFELP Loan ABCP Facilities [Member]
Debt Instrument [Line Items]
Total	1,900
Private Education Loan ABCP Facilities [Member]
Debt Instrument [Line Items]
Total	2,100
Total Before Hedge Accounting Adjustments [Member]
Debt Instrument [Line Items]
Short-term borrowings, Carrying Value	$ 4,235	$ 5,880
Short-term Weighted Average Interest Rate	6.66%	5.78%
Long-term borrowings, Carrying Value	$ 53,680	$ 61,516
Long-term Weighted Average Interest Rate	5.59%	4.66%
Total	$ 57,915	$ 67,396
Total Before Hedge Accounting Adjustments [Member] | Senior Unsecured Debt [Member]
Debt Instrument [Line Items]
Short-term borrowings, Carrying Value	$ 506	$ 1,301
Short-term Weighted Average Interest Rate	5.88%	5.90%
Long-term borrowings, Carrying Value	$ 5,351	$ 5,711
Long-term Weighted Average Interest Rate	6.61%	5.82%
Total	$ 5,857	$ 7,012
Total Before Hedge Accounting Adjustments [Member] | Total Unsecured Borrowings [Member]
Debt Instrument [Line Items]
Short-term borrowings, Carrying Value	$ 506	$ 1,301
Short-term Weighted Average Interest Rate	5.88%	5.90%
Long-term borrowings, Carrying Value	$ 5,351	$ 5,711
Long-term Weighted Average Interest Rate	6.61%	5.82%
Total	$ 5,857	$ 7,012
Total Before Hedge Accounting Adjustments [Member] | FFELP Loan Securitizations [Member]
Debt Instrument [Line Items]
Short-term borrowings, Carrying Value	$ 59	$ 76
Short-term Weighted Average Interest Rate	6.84%	6.01%
Long-term borrowings, Carrying Value	$ 35,626	$ 42,675
Long-term Weighted Average Interest Rate	6.06%	4.96%
Total	$ 35,685	$ 42,751
Total Before Hedge Accounting Adjustments [Member] | Private Education Loan Securitizations [Member]
Debt Instrument [Line Items]
Short-term borrowings, Carrying Value	$ 435	$ 725
Short-term Weighted Average Interest Rate	8.14%	7.17%
Long-term borrowings, Carrying Value	$ 11,754	$ 12,744
Long-term Weighted Average Interest Rate	3.59%	3.11%
Total	$ 12,189	$ 13,469
Total Before Hedge Accounting Adjustments [Member] | FFELP Loan ABCP Facilities [Member]
Debt Instrument [Line Items]
Short-term borrowings, Carrying Value	$ 1,854	$ 923
Short-term Weighted Average Interest Rate	6.60%	5.31%
Long-term borrowings, Carrying Value	$ 89	$ 386
Long-term Weighted Average Interest Rate	6.29%	5.33%
Total	$ 1,943	$ 1,309
Total Before Hedge Accounting Adjustments [Member] | Private Education Loan ABCP Facilities [Member]
Debt Instrument [Line Items]
Short-term borrowings, Carrying Value	$ 1,286	$ 2,734
Short-term Weighted Average Interest Rate	6.62%	5.55%
Long-term borrowings, Carrying Value	$ 821	$ 0
Long-term Weighted Average Interest Rate	6.84%	0.00%
Total	$ 2,107	$ 2,734
Total Before Hedge Accounting Adjustments [Member] | Other [Member]
Debt Instrument [Line Items]
Short-term borrowings, Carrying Value	$ 95	$ 121
Short-term Weighted Average Interest Rate	5.61%	4.61%
Long-term borrowings, Carrying Value	$ 39	$ 0
Long-term Weighted Average Interest Rate	5.50%	0.00%
Total	$ 134	$ 121
Total Before Hedge Accounting Adjustments [Member] | Secured Borrowings [Member]
Debt Instrument [Line Items]
Short-term borrowings, Carrying Value	$ 3,729	$ 4,579
Short-term Weighted Average Interest Rate	6.76%	5.74%
Long-term borrowings, Carrying Value	$ 48,329	$ 55,805
Long-term Weighted Average Interest Rate	5.47%	4.54%
Total	$ 52,058	$ 60,384
Hedge Accounting Adjustments [Member]
Debt Instrument [Line Items]
Short-term borrowings, Carrying Value	$ (9)	$ (10)
Short-term Weighted Average Interest Rate	0.01%	0.01%
Long-term borrowings, Carrying Value	$ (278)	$ (490)
Long-term Weighted Average Interest Rate	0.03%	0.04%
Total	$ (287)	$ (500)