Derivative and Other Hedging Instruments (Effect Of Derivative Instruments Not Designated As Hedges On Income Statement) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended														3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Mar. 31, 2013 Purchases Of TBAs And Forward Settling Agency Securities [Member]	Mar. 31, 2012 Purchases Of TBAs And Forward Settling Agency Securities [Member]	Mar. 31, 2013 Sale Of TBA And Forward Settling Agency Securities [Member]	Mar. 31, 2012 Sale Of TBA And Forward Settling Agency Securities [Member]	Mar. 31, 2013 Payer Interest Rate Swaps [Member]	Mar. 31, 2012 Payer Interest Rate Swaps [Member]	Mar. 31, 2013 Payer Swaption [Member]	Mar. 31, 2012 Payer Swaption [Member]	Mar. 31, 2013 Short Sales Of U S Government Securities [Member]	Mar. 31, 2012 Short Sales Of U S Government Securities [Member]	Mar. 31, 2012 Treasury Futures [Member]	Dec. 31, 2011 Treasury Futures [Member]	Mar. 31, 2013 Treasury Futures Short [Member]	Mar. 31, 2012 Treasury Futures Short [Member]	Mar. 31, 2012 Markit IOS Total Return Swaps - Long [Member]	Mar. 31, 2012 Markit IOS Total Return Swaps - Short [Member]
Unrealized Gain On Derivative Instrument And Trading Securities	$ (1)	$ 1
Notional Amount			21,855	3,699	9,378	3,803	46,850	30,250	14,450	3,200	11,835	880	1,653	783	0		41	206
Additions			77,600	22,313	34,333	30,829	5,750	7,850	11,150	7,950	9,935	10,990			800		0	0
Settlement, Expirations or Exercise			(70,261)	(24,225)	(40,785)	(25,579)	(1,350)	0	(2,700)	(650)	(9,210)	(8,005)			0
Notional Amount			29,194	1,787	2,926	9,053	51,250	38,100	22,900	10,500	12,560	3,865	1,653	783	800		39	194
Amount Gain/(Loss) Recognized in Income on Derivatives	$ (110)	$ 46	$ (185)	$ 67	$ 83	$ (51)	$ 54	$ (44)	$ (44)	$ 3	$ (3)	$ 52			$ (15)	$ 21	$ 1	$ (3)