Long-Term Borrowings (Narrative) (Details) (USD $)
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6 Months Ended | 3 Months Ended | 6 Months Ended | 0 Months Ended | 3 Months Ended | 6 Months Ended | |||||||||||||
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Jun. 30, 2013
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Jun. 30, 2012
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Dec. 31, 2012
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Dec. 31, 2012
Fixed Rate Senior Notes Due November 2022 [Member]
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Jun. 30, 2012
Fixed Rate Senior Notes Due April 2022 [Member]
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Jun. 30, 2013
Parent Company [Member]
Fixed Rate Senior Notes Due November 2022 [Member]
Corporate Debt Securities [Member]
|
Dec. 31, 2012
Parent Company [Member]
Fixed Rate Senior Notes Due November 2022 [Member]
Corporate Debt Securities [Member]
|
Jun. 30, 2013
Parent Company [Member]
Fixed Rate Senior Notes Due November 2022 [Member]
Corporate Debt Securities [Member]
|
May 08, 2012
Parent Company [Member]
Fixed Rate Senior Notes Due April 2022 [Member]
Corporate Debt Securities [Member]
|
Apr. 27, 2012
Parent Company [Member]
Fixed Rate Senior Notes Due April 2022 [Member]
Corporate Debt Securities [Member]
|
Jun. 30, 2013
Parent Company [Member]
Fixed Rate Senior Notes Due April 2022 [Member]
Corporate Debt Securities [Member]
|
Jun. 30, 2012
Parent Company [Member]
Fixed Rate Senior Notes Due April 2022 [Member]
Corporate Debt Securities [Member]
|
Jun. 30, 2013
Parent Company [Member]
Fixed Rate Senior Notes Due April 2022 [Member]
Corporate Debt Securities [Member]
|
Jun. 30, 2012
Parent Company [Member]
Fixed Rate Senior Notes Due April 2022 [Member]
Corporate Debt Securities [Member]
|
Dec. 31, 2012
Parent Company [Member]
Fixed Rate Senior Notes Due April 2022 [Member]
Corporate Debt Securities [Member]
|
Jun. 30, 2013
Discover Card Master Trust I and Discover Card Execution Note Trust [Member]
Secured Debt [Member]
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Dec. 31, 2012
Discover Card Master Trust I and Discover Card Execution Note Trust [Member]
Secured Debt [Member]
|
Jun. 30, 2013
Discover Card Master Trust I and Discover Card Execution Note Trust [Member]
Floating Rate Asset Backed Securities And Other Borrowings [Member]
Secured Debt [Member]
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Dec. 31, 2012
Discover Card Master Trust I and Discover Card Execution Note Trust [Member]
Floating Rate Asset Backed Securities And Other Borrowings [Member]
Secured Debt [Member]
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Debt Instrument [Line Items] | |||||||||||||||||||
Exchange of Debt, Amount, New Notes | $ 500,000,000 | $ 14,000,000 | $ 308,000,000 | $ 322,000,000 | |||||||||||||||
Premium paid on debt exchange | 0 | 114,000,000 | 176,000,000 | 115,000,000 | |||||||||||||||
Amortization of Premium Paid on Debt Exchange | 3,000,000 | 6,000,000 | 1,000,000 | 1,000,000 | 3,000,000 | 1,000,000 | |||||||||||||
Total commitment of secured credit facilities | 7,500,000,000 | ||||||||||||||||||
Long-term borrowings | $ 18,033,000,000 | $ 17,666,000,000 | $ 329,000,000 | $ 324,000,000 | $ 329,000,000 | $ 215,000,000 | $ 215,000,000 | $ 211,000,000 | $ 13,578,000,000 | $ 13,773,000,000 | $ 500,000,000 | $ 750,000,000 |