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Subsequent Events (Details) - Commercial Paper - ABCP borrowings - USD ($) | Feb. 21, 2019 | Feb. 21, 2018
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Subsequent Event [Line Items] |  |
Private education loan funding |  | $ 750,000,000.0
Subsequent Event |  |
Subsequent Event [Line Items] |  |
Private education loan funding | $ 750,000,000.0 |
Minimum |  |
Subsequent Event [Line Items] |  |
Unused borrowing capacity fee (as a percent) |  | 0.35%
Minimum | Subsequent Event |  |
Subsequent Event [Line Items] |  |
Unused borrowing capacity fee (as a percent) | 0.35% |
Maximum |  |
Subsequent Event [Line Items] |  |
Unused borrowing capacity fee (as a percent) |  | 0.45%
Maximum | Subsequent Event |  |
Subsequent Event [Line Items] |  |
Unused borrowing capacity fee (as a percent) | 0.45% |
London Interbank Offered Rate (LIBOR) |  |
Subsequent Event [Line Items] |  |
Basis spread on variable rate |  | 0.85%
London Interbank Offered Rate (LIBOR) | Subsequent Event |  |
Subsequent Event [Line Items] |  |
Basis spread on variable rate | 0.85% |

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- Definition Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.19(b),22(b)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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- Definition Detail information of subsequent event by type. User is expected to use existing line items from elsewhere in the taxonomy as the primary line items for this disclosure, which is further associated with dimension and member elements pertaining to a subsequent event. + References No definition available. + Details
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