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Long-Term Borrowings (Narrative) (Details) (Discover Card Master Trust I and Discover Card Execution Note Trust [Member], Secured Debt [Member], USD $)
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Mar. 31, 2015
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|---|---|
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Discover Card Master Trust I and Discover Card Execution Note Trust [Member] | Secured Debt [Member]
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| Debt Instrument [Line Items] | |
| Total commitment of secured credit facilities | $ 7,500,000,000 |
| Total used commitment of secured credit facilities | $ 0 |