Derivative and Other Hedging Instruments (Narrative) (Details) (USD $)	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Derivative Instruments, Gain Reclassified from Accumulated OCI into Income, Effective Portion									$ 252,000,000	$ 35,000,000
Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Derivatives Arising During Period, Net of Tax		51,000,000	52,000,000	52,000,000	54,000,000	(513,000,000)	(252,000,000)	61,000,000	205,000,000	(650,000,000)	(24,000,000)
Net Periodic Interest Rate Costs on Swaps									457,000,000	(89,000,000)
Fair Value of Derivative Instruments	95,000,000				13,000,000				95,000,000	13,000,000
Obligation to return securities borrowed under reverse repurchase agreements, at fair value	11,763,000,000				899,000,000				11,763,000,000	899,000,000
Proceeds from sales of treasury securities									11,700,000,000	880,000,000
Interest rate swap agreement outstanding not designated as hedge					3,200,000,000					3,200,000,000
Gain on interest only securities remeasured at fair value through earnings									17,000,000	17,000,000	1,000,000
Loss on interest only securities remeasured at fair value through earnings									17,000,000	17,000,000	1,000,000
Loss on cash flow hedge ineffectiveness										2,000,000
Gain on trading securities									(17,000,000)	(16,000,000)	1,000,000
Restricted Cash Pledged As Collateral	249,000,000								249,000,000
Unrealized Gain (Loss) On Derivative Instrument And Trading Securities	89,000,000	(460,000,000)	(1,029,000,000)	47,000,000	(137,000,000)	(222,000,000)	(100,000,000)	12,000,000	(1,353,000,000)	(447,000,000)	38,000,000
Interest Rate Swap [Member]
Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Derivatives Arising During Period, Net of Tax										(650,000,000)	(24,000,000)
Interest Rate Contract [Member]
Fair value of interest rate swap, liability position	1,200,000,000								1,200,000,000
Agency securities, pledged as collateral against interest rate swap	1,100,000,000								1,100,000,000
Discontinuation of Election to Account for Interest Rate Swaps as Designated Cash Flow Hedges [Member]
Deferred Gain (Loss) on Discontinuation of Interest Rate Fair Value Hedge	486,000,000								486,000,000
Deferred gain loss discontinued interest rate swap expected to be reclassified from OCI to interest expense next twelve months									189,000,000
Discontinuation of Election to Account for Interest Rate Swaps as Designated Cash Flow Hedges [Member] | Interest Rate Swap [Member]
Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Derivatives Arising During Period, Net of Tax	$ 50,000,000								$ 205,000,000	$ 54,000,000