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Securities Available for Sale and Securities Held to Maturity - Additional Information (Detail) (USD $)
In Millions, unless otherwise specified |
3 Months Ended | 9 Months Ended | ||||||||||
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Sep. 30, 2012
CreditScore
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Sep. 30, 2011
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Sep. 30, 2012
CreditScore
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Sep. 30, 2011
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Dec. 31, 2011
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Dec. 31, 2010
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| Schedule of Available-for-sale Securities [Line Items] | ||||||||||||
| Securities available for sale Gross Unrealized Losses | $ 88 | $ 88 | $ 273 | |||||||||
| Fair Isaac & Company minimum credit score for Prime loan origination | 620 | 620 | ||||||||||
| Securities available for sale Amortized Cost | 41,948 | 41,948 | 33,950 | |||||||||
| Securities available for sale | 42,448 | 42,448 | 33,965 | |||||||||
| Cash and cash equivalents | 8,523 | 6,376 | 8,523 | 6,376 | 8,679 | 4,931 | ||||||
| Loan-to-deposit ratio | 15.00% | 15.00% | ||||||||||
| Net impairment losses on securities | 3 | [1] | 13 | [1] | 28 | [1] | 22 | [1] | ||||
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Alt-A residential mortgage backed securities
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| Schedule of Available-for-sale Securities [Line Items] | ||||||||||||
| Securities available for sale Amortized Cost | 326 | 326 | ||||||||||
| Securities available for sale | $ 280 | $ 280 | ||||||||||
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