Borrowings - Company's Borrowings (Detail) - USD ($) $ in Millions	Mar. 31, 2023	Dec. 31, 2022
Debt Instrument [Line Items]
Short-term borrowings	$ 5,753	$ 5,870
Long-term borrowings	57,388	61,026
Total	63,141	66,896
Total Before Hedge Accounting Adjustments [Member]
Debt Instrument [Line Items]
Short-term borrowings	5,774	5,880
Long-term borrowings	57,754	61,516
Total	63,528	67,396
Total Before Hedge Accounting Adjustments [Member] | Senior Unsecured Debt [Member]
Debt Instrument [Line Items]
Short-term borrowings	1,149	1,301
Long-term borrowings	4,864	5,711
Total	6,013	7,012
Total Before Hedge Accounting Adjustments [Member] | Total Unsecured Borrowings [Member]
Debt Instrument [Line Items]
Short-term borrowings	1,149	1,301
Long-term borrowings	4,864	5,711
Total	6,013	7,012
Total Before Hedge Accounting Adjustments [Member] | FFELP Loan Securitizations [Member]
Debt Instrument [Line Items]
Short-term borrowings	68	76
Long-term borrowings	40,275	42,675
Total	40,343	42,751
Total Before Hedge Accounting Adjustments [Member] | Private Education Loan Securitizations [Member]
Debt Instrument [Line Items]
Short-term borrowings	648	725
Long-term borrowings	12,187	12,744
Total	12,835	13,469
Total Before Hedge Accounting Adjustments [Member] | FFELP Loan ABCP Facilities [Member]
Debt Instrument [Line Items]
Short-term borrowings	887	923
Long-term borrowings	428	386
Total	1,315	1,309
Total Before Hedge Accounting Adjustments [Member] | Private Education Loan ABCP Facilities [Member]
Debt Instrument [Line Items]
Short-term borrowings	2,917	2,734
Long-term borrowings	0	0
Total	2,917	2,734
Total Before Hedge Accounting Adjustments [Member] | Other [Member]
Debt Instrument [Line Items]
Short-term borrowings	105	121
Long-term borrowings	0	0
Total	105	121
Total Before Hedge Accounting Adjustments [Member] | Secured Borrowings [Member]
Debt Instrument [Line Items]
Short-term borrowings	4,625	4,579
Long-term borrowings	52,890	55,805
Total	57,515	60,384
Hedge Accounting Adjustments [Member]
Debt Instrument [Line Items]
Short-term borrowings	(21)	(10)
Long-term borrowings	(366)	(490)
Total	$ (387)	$ (500)