Derivative and Other Hedging Instruments (Effect Of Derivative Instruments Not Designated As Hedges On Comprehensive Income Statement) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Mar. 31, 2020	Dec. 31, 2019	Mar. 31, 2019	Dec. 31, 2018
Changes in Derivative and Other Hedge Portfolio [Roll Forward]
Amount Gain/(Loss) Recognized in Income on Derivatives	$ (237)	$ (1,437)	$ (3,417)	$ (2,433)
Interest Rate Swaption [Member]
Changes in Derivative and Other Hedge Portfolio [Roll Forward]
Notional Amount	(9,350)	(4,400)	(9,350)	(4,400)	$ (9,550)	$ (8,850)	$ (2,550)
Additions	0	(2,650)	(2,000)	(2,650)
Settlement, Expirations or Exercise	200	800	1,500	1,750
Notional Amount	(9,350)		(9,350)
Amount Gain/(Loss) Recognized in Income on Derivatives	(14)	(25)	(148)	(52)
TBA and Forward Settling Agency Securities [Member]
Changes in Derivative and Other Hedge Portfolio [Roll Forward]
Notional Amount	(19,760)	(11,043)	(19,760)	(11,043)	(20,279)	(7,322)	(6,822)	$ (7,152)
Additions	(75,186)	(27,859)	(112,936)	(46,301)
Settlement, Expirations or Exercise				42,410
Amount Gain/(Loss) Recognized in Income on Derivatives	220	163	913	246
Purchases Of TBAs And Forward Settling Agency Securities [Member]
Changes in Derivative and Other Hedge Portfolio [Roll Forward]
Settlement, Expirations or Exercise	75,705	23,638	100,498
Interest Rate Swap [Member]
Changes in Derivative and Other Hedge Portfolio [Roll Forward]
Additions	(25,750)	(65,000)	(75,725)	(70,350)
Settlement, Expirations or Exercise	30,150	38,225	112,725	47,025
Notional Amount	(42,075)		(42,075)
Amount Gain/(Loss) Recognized in Income on Derivatives	(379)	(1,019)	(3,174)	(1,615)
US Treasury Securities [Member]
Changes in Derivative and Other Hedge Portfolio [Roll Forward]
Amount Gain/(Loss) Recognized in Income on Derivatives	(8)	(57)	(112)	(88)
Not Designated as Hedging Instrument [Member] | Interest Rate Swaption [Member]
Changes in Derivative and Other Hedge Portfolio [Roll Forward]
Notional Amount								(3,500)
Not Designated as Hedging Instrument [Member] | Interest Rate Swap [Member]
Changes in Derivative and Other Hedge Portfolio [Roll Forward]
Notional Amount	(42,075)	(74,950)	(42,075)	(74,950)	(46,475)	(79,075)	(48,175)	(51,625)
Short [Member] | US Treasury Securities [Member]
Changes in Derivative and Other Hedge Portfolio [Roll Forward]
Notional Amount	(7,247)	(7,245)	(7,247)	(7,245)	(4,245)	(9,224)	(18,735)	(21,345)
Additions	(4,187)	(2,536)	(10,232)	(7,306)
Settlement, Expirations or Exercise	(1,185)	(14,026)	(12,209)	21,406
Amount Gain/(Loss) Recognized in Income on Derivatives	(60)	(505)	(997)	(930)
Long [Member] | US Treasury Securities [Member]
Changes in Derivative and Other Hedge Portfolio [Roll Forward]
Amount Gain/(Loss) Recognized in Income on Derivatives	4	6	101	6
Debt Securities, Trading, and Equity Securities, FV-NI	1,132	1,134	1,132	1,134	3,569	95	120	45
Trading Securities Added During the Period	550	1,018	7,011	1,423
Notional Amount Of Trading Securities Settlement Expiration During The Period	(2,987)	(4)	(5,974)	(334)
Future [Member] | Short [Member] | US Treasury Securities [Member]
Changes in Derivative and Other Hedge Portfolio [Roll Forward]
Notional Amount	(1,000)	(1,650)	(1,000)	(1,650)	$ (1,000)	$ (1,000)	$ (1,650)	$ (1,650)
Additions	1,000	1,650	2,000	(3,300)
Settlement, Expirations or Exercise	$ (1,000)	$ (1,650)	$ (2,000)	$ 3,300