Derivative and Other Hedging Instruments (Effect Of Derivative Instruments Not Designated As Hedges On Income Statement) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Unrealized Gain On Derivative Instrument And Trading Securities	$ 17	$ 16	$ (1)
Amount Gain/(Loss) Recognized in Income on Derivatives	(1,341)	(462)	44
Put Option [Member]
Additions		200	75
Settlement, Expirations or Exercise		(200)	(75)
Purchases Of TBAs And Forward Settling Agency Securities [Member]
Notional Amount	3,700	512	597
Additions	140,731	51,488	6,662
Settlement, Expirations or Exercise	(122,576)	(48,300)	(6,747)
Notional Amount	21,855	3,700	512
Amount Gain/(Loss) Recognized in Income on Derivatives	444	160	19
Sale Of TBA And Forward Settling Agency Securities [Member]
Notional Amount	3,803	1,361	617
Additions	176,905	100,077	16,937
Settlement, Expirations or Exercise	(171,330)	(97,635)	(16,193)
Notional Amount	9,378	3,803	1,361
Amount Gain/(Loss) Recognized in Income on Derivatives	(413)	(302)	11
Put Option [Member]
Amount Gain/(Loss) Recognized in Income on Derivatives		1
Payer Interest Rate Swaps [Member]
Notional Amount	30,250	50	0
Additions	25,000	6,750	350
Additions Due to Hedge De-Designations		23,900
Settlement, Expirations or Exercise	(8,400)	(450)	(300)
Notional Amount	46,850	30,250	50
Amount Gain/(Loss) Recognized in Income on Derivatives	(1,034)	(119)	(3)
Payer Swaption [Member]
Notional Amount	3,200	850	200
Additions	18,250	5,600	850
Settlement, Expirations or Exercise	(7,000)	(3,250)	(200)
Notional Amount	14,450	3,200	850
Amount Gain/(Loss) Recognized in Income on Derivatives	(106)	(63)	19
Receiver Swaption [Member]
Notional Amount			100
Additions		250	300
Settlement, Expirations or Exercise		(250)	(400)
Amount Gain/(Loss) Recognized in Income on Derivatives		(1)	0
Short Sales Of U S Government Securities [Member]
Notional Amount	880	250
Additions	36,555	15,794	750
Settlement, Expirations or Exercise	(25,600)	(15,164)	(500)
Notional Amount	11,835	880	250
Amount Gain/(Loss) Recognized in Income on Derivatives	(142)	(133)	(2)
Treasury Futures [Member]
Notional Amount	783
Additions	3,838
Settlement, Expirations or Exercise	(4,621)
Notional Amount	0
Amount Gain/(Loss) Recognized in Income on Derivatives	(90)
Treasury Futures Short [Member]
Notional Amount		783
Amount Gain/(Loss) Recognized in Income on Derivatives		(12)
Markit IOS Total Return Swaps - Long [Member]
Notional Amount	41
Additions	0	1,195
Settlement, Expirations or Exercise	(41)
Notional Amount	0	41
Amount Gain/(Loss) Recognized in Income on Derivatives	0	(7)
Markit IOS Total Return Swaps - Short [Member]
Notional Amount	206
Additions	0	685
Settlement, Expirations or Exercise	(206)
Notional Amount	0	206
Amount Gain/(Loss) Recognized in Income on Derivatives	$ 0	$ 14