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Borrowings - Company's Borrowings (Detail) - USD ($) $ in Millions | Mar. 31, 2017 | Dec. 31, 2016
--- | --- | ---
Debt Instrument [Line Items] |  |
Short-term borrowings | $ 2,160 | $ 2,334
Long-term borrowings | 109,586 | 112,368
Total | 111,746 | 114,702
Total Before Hedge Accounting Adjustments [Member] |  |
Debt Instrument [Line Items] |  |
Short-term borrowings | 2,161 | 2,335
Long-term borrowings | 110,223 | 113,119
Total | 112,384 | 115,454
Total Before Hedge Accounting Adjustments [Member] | Senior Unsecured Debt [Member] |  |
Debt Instrument [Line Items] |  |
Short-term borrowings | 571 | 717
Long-term borrowings | 13,424 | 13,029
Total | 13,995 | 13,746
Total Before Hedge Accounting Adjustments [Member] | Total Unsecured Borrowings [Member] |  |
Debt Instrument [Line Items] |  |
Short-term borrowings | 571 | 717
Long-term borrowings | 13,424 | 13,029
Total | 13,995 | 13,746
Total Before Hedge Accounting Adjustments [Member] | FFELP Loan Securitizations [Member] |  |
Debt Instrument [Line Items] |  |
Long-term borrowings | 73,047 | 73,522
Total | 73,047 | 73,522
Total Before Hedge Accounting Adjustments [Member] | Private Education Loan Securitizations [Member] |  |
Debt Instrument [Line Items] |  |
Short-term borrowings | 548 | 548
Long-term borrowings | 13,343 | 14,125
Total | 13,891 | 14,673
Total Before Hedge Accounting Adjustments [Member] | FFELP Loan - Other Facilities [Member] |  |
Debt Instrument [Line Items] |  |
Long-term borrowings | 10,409 | 12,443
Total | 10,409 | 12,443
Total Before Hedge Accounting Adjustments [Member] | Private Education Loan - Other Facilities [Member] |  |
Debt Instrument [Line Items] |  |
Short-term borrowings | 540 | 464
Total | 540 | 464
Total Before Hedge Accounting Adjustments [Member] | Other [Member] |  |
Debt Instrument [Line Items] |  |
Short-term borrowings | 502 | 606
Total | 502 | 606
Total Before Hedge Accounting Adjustments [Member] | Secured Borrowings [Member] |  |
Debt Instrument [Line Items] |  |
Short-term borrowings | 1,590 | 1,618
Long-term borrowings | 96,799 | 100,090
Total | 98,389 | 101,708
Hedge Accounting Adjustments [Member] |  |
Debt Instrument [Line Items] |  |
Short-term borrowings | (1) | (1)
Long-term borrowings | (637) | (751)
Total | $ (638) | $ (752)

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