Securities Available for Sale (Schedule of Amortized Cost and Fair Value of Available for Sale Debt Securities by Contractual Date) (Details) (USD $) In Millions, unless otherwise specified	6 Months Ended
Jun. 30, 2012
Amortized Cost, Total	$ 31,174
Fair Value, Total	31,437
Annualized Average Yield, Total	1.00%
U.S. Government and Agency Securities
Amortized Cost, Total	26,864
Fair Value, Total	27,112
Annualized Average Yield, Total	1.00%
U.S. Treasury Securities
Amortized Cost, Due within 1 year	1,151
Fair Value, Due within 1 year	1,160
Annualized Average Yield, Due within 1 year	1.40%
Amortized Cost, After 1 year but through 5 years	9,691
Fair Value, After 1 year but through 5 years	9,807
Annualized Average Yield, After 1 year but through 5 years	0.90%
Amortized Cost, After 5 years	572
Fair value, After 5 years	589
Annualized Average Yield, After 5 years	1.40%
Amortized Cost, Total	11,414
Fair Value, Total	11,556
U.S. Agency Securities
Amortized Cost, After 5 years	15,450
Fair value, After 5 years	15,556
Amortized Cost, Total	15,450
Fair Value, Total	15,556
Annualized Average Yield, Total	1.10%
Corporate and Other Debt
Amortized Cost, Total	4,310
Fair Value, Total	4,325
Annualized Average Yield, Total	1.10%
Auto Loan Asset-backed Securities
Amortized Cost, Due within 1 year	0
Fair Value, Due within 1 year	0
Amortized Cost, After 1 year but through 5 years	895
Fair Value, After 1 year but through 5 years	897
Annualized Average Yield, After 1 year but through 5 years	0.80%
Amortized Cost, After 5 years	19
Fair value, After 5 years	19
Annualized Average Yield, After 5 years	1.00%
Amortized Cost, Total	914
Fair Value, Total	916
Corporate Bonds
Amortized Cost, Due within 1 year	81
Fair Value, Due within 1 year	81
Annualized Average Yield, Due within 1 year	0.60%
Amortized Cost, After 1 year but through 5 years	1,366
Fair Value, After 1 year but through 5 years	1,370
Annualized Average Yield, After 1 year but through 5 years	1.10%
Amortized Cost, After 5 years	21
Fair value, After 5 years	21
Annualized Average Yield, After 5 years	1.70%
Amortized Cost, Total	1,468
Fair Value, Total	1,472
FFELP Student Loan Asset-backed Securities
Amortized Cost, Due within 1 year	0
Fair Value, Due within 1 year	0
Amortized Cost, After 1 year but through 5 years	23
Fair Value, After 1 year but through 5 years	23
Annualized Average Yield, After 1 year but through 5 years	0.80%
Amortized Cost, After 5 years	1,905
Fair value, After 5 years	1,914
Annualized Average Yield, After 5 years	1.20%
Amortized Cost, Total	1,928
Fair Value, Total	$ 1,937

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