Derivative and Other Hedging Instruments (Derivative and Other Hedging Instrument Assets (Liabilities), at Fair Value) (Details) (USD $)	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013
Derivative [Line Items]
Derivative Instruments Not Designated as Hedging Instruments, Asset, at Fair Value	$ 408,000,000	$ 1,194,000,000
Derivative Instruments Not Designated as Hedging Instruments, Liability, at Fair Value	890,000,000	422,000,000
Derivative assets, at fair value	408,000,000us-gaap_DerivativeAssets	1,194,000,000us-gaap_DerivativeAssets
U.S. Treasury securities, at fair value (including pledged securities of $2,375 and $3,778, respectively)	2,427,000,000	3,822,000,000
Financial Instruments Sold, Not yet Purchased, US Government and Agency Obligations	(5,363,000,000)	(1,848,000,000)
government bonds owned and sold short net	(2,936,000,000)	1,974,000,000
Proceeds from Securities Purchased under Agreements to Resell	5,400,000,000	1,900,000,000
Interest Rate Swap [Member]
Derivative [Line Items]
Derivative Instruments Not Designated as Hedging Instruments, Liability, at Fair Value	880,000,000	400,000,000
Interest Rate Swap [Member] \| Fair Value, Inputs, Level 2 [Member]
Derivative [Line Items]
Derivative Instruments Not Designated as Hedging Instruments, Asset, at Fair Value	136,000,000	880,000,000
Interest Rate Swaption [Member] \| Fair Value, Inputs, Level 2 [Member]
Derivative [Line Items]
Derivative Instruments Not Designated as Hedging Instruments, Asset, at Fair Value	75,000,000	258,000,000
Purchases Of TBAs And Forward Settling Agency Securities [Member]
Derivative [Line Items]
Derivative Instruments Not Designated as Hedging Instruments, Asset, at Fair Value		17,000,000
Derivative Instruments Not Designated as Hedging Instruments, Liability, at Fair Value	5,000,000	22,000,000
Future [Member] \| Fair Value, Inputs, Level 1 [Member] \| US Treasury Securities [Member]
Derivative [Line Items]
Derivative Instruments Not Designated as Hedging Instruments, Liability, at Fair Value	5,000,000	39,000,000
TBA and Forward Settling Agency Securities [Member] \| Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 2 [Member]
Derivative [Line Items]
Derivative assets, at fair value		17,000,000
TBA and Forward Settling Agency Securities [Member] \| Fair Value, Measurements, Recurring [Member] \| Purchases Of TBAs And Forward Settling Agency Securities [Member] \| Fair Value, Inputs, Level 2 [Member]
Derivative [Line Items]
Derivative assets, at fair value	$ 197,000,000

government bonds owned and sold short net

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- Definition

Fair value, after the effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets not subject to a master netting arrangement and not elected to be offset.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 825

-SubTopic 10

-Section 50

-Paragraph 10

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=35750535&loc=d3e13433-108611

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 10

-Section 45

-Paragraph 5

-URI http://asc.fasb.org/extlink&oid=6945355&loc=d3e41228-113958

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 825

-SubTopic 10

-Section 50

-Paragraph 15

-URI http://asc.fasb.org/extlink&oid=35750535&loc=d3e13495-108611

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 20

-Section 50

-Paragraph 3

-Subparagraph (c)

-URI http://asc.fasb.org/extlink&oid=34720828&loc=SL20225862-175312

Reference 5: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

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-Paragraph 6

-URI http://asc.fasb.org/extlink&oid=6945355&loc=d3e41271-113958

Reference 6: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 20

-Section 55

-Paragraph 10

-URI http://asc.fasb.org/extlink&oid=36459792&loc=SL20226008-175313

+ Details

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- Definition

Fair value as of the balance sheet date of derivative instrument not designated as hedging instrument and classified as an asset.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 10

-Section 50

-Paragraph 4B

-Subparagraph (c)(2)

-URI http://asc.fasb.org/extlink&oid=35706170&loc=SL5624163-113959

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- Definition

Fair value as of the balance sheet date of derivative instrument not designated as hedging instrument and classified as a liability.

+ References

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- Definition

The fair value as of the balance sheet date of firm holdings in debt obligations issued by the US government including short-term Treasury bills, medium-term Treasury notes, and long-term Treasury bonds, as well as debt issued by agencies. Includes both pledged (to counterparties as collateral for financing transactions) and unpledged holdings.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 940

-SubTopic 320

-Section 45

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=35711157&loc=d3e42546-110969

+ Details

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- Definition

Fair value of obligations arising from US treasury and other US government and agency debt obligations sold short.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 940

-SubTopic 320

-Section 35

-Paragraph 1

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=35711043&loc=d3e42429-110968

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- Definition

The cash inflow associated with agreements to purchase and then resell securities to counterparties (reverse repurchase agreements).

+ References

No definition available.

+ Details

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