Investment Securities - Additional Information (Details) (USD $)	9 Months Ended	12 Months Ended
Sep. 30, 2014	Dec. 31, 2013
Schedule of Available-for-sale Securities [Line Items]
Number of sale securities exceeding amortized cost over fair value	550
Amortized cost exceeding fair value	$ 312,000,000	$ 631,000,000
Difference in amortized cost and fair value of securities that had been in a loss position for 12 months or longer	271,000,000	109,000,000
Securities held to maturity	30
Difference in carrying value and fair value	13,000,000
Fair value of securities pledged	5,800,000,000	10,700,000,000
Carrying value of securities pledged	13,700,000,000	8,200,000,000
Encumbered amount of securities pledged as collateral	11,300,000,000	17,300,000,000
Fair value of securities pledged, accepted	63,000,000	53,000,000
US Treasury and Government [Member] \| Investment Securities Portfolio
Schedule of Available-for-sale Securities [Line Items]
Percentage of portfolio	85.00%	77.00%
Non-agency RMBS and CMBS, Non-agency ABS and Other Securities \| Gross Unrealized Losses on Available-for-sale Securities
Schedule of Available-for-sale Securities [Line Items]
Percentage of portfolio	24.00%
Non-agency RMBS and CMBS, Non-agency ABS and Other Securities
Schedule of Available-for-sale Securities [Line Items]
Amortized cost exceeding fair value	$ 76,000,000

Amount of accumulated unrealized loss on investments in debt and equity securities classified as available-for-sale that have been in a continuous loss position for twelve months or longer.

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Amount of accumulated unrealized loss on investments in debt and equity securities classified as available-for-sale in a continuous loss position.

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Number of investment positions in available-for-sale investments in a continuous unrealized loss position for which an other-than-temporary impairment (OTTI) has not been recognized in the income statement.

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The fair value of available-for-sale securities that serve as collateral for borrowings.

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For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division.

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Amount of obligation to return securities collateral under master netting arrangements that have not been offset against derivative assets.

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Amount of accumulated unrealized loss on investments in debt securities classified as held-to-maturity in a continuous loss position.

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Disclosure regarding factors used to determine that the impairment of securities categorized as held-to-maturity where cost exceeds fair value is not an other than temporary impairment (OTTI). This item contains disclosure of the number of investment positions in the held-to-maturity investments determined to be temporarily impaired.

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The carrying amount of held-to-maturity securities that serve as collateral for borrowings.

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Total debt and equity financial instruments including: (1) securities held-to-maturity, (2) trading securities, and (3) securities available-for-sale that are pledged to one or more secured parties who have the right to buy, sell, or re-pledge the collateral.

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