Repurchase Agreements And Reverse Repurchase Agreements (Narrative) (Details) $ in Millions	Mar. 31, 2020 USD ($) days	Dec. 31, 2019 USD ($) days
Assets Sold under Agreements to Repurchase [Line Items]
Receivable Under Reverse Repurchase Agreements	$ 4,938	$ 10,181
Securities Sold under Agreements to Repurchase	66,540	89,182
Obligation to Return Securities Borrowed Under Reverse Repurchase Agreements at Fair Value	$ 4,886	$ 9,543
Short-term Debt, Weighted Average Interest Rate, at Point in Time	1.33%	2.17%
Debt of consolidated variable interest entities, at fair value	$ (214)	$ (228)
TBA securities Fifteen Year and Thirty Year Securities [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Derivative, Fair Value, Net	574	25
TBA and Forward Settling Agency Securities [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Derivative, Forward Settlement Value	20,648	7,404
Derivative, Fair Value, Net	574	25
Maturity Overnight [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Securities Sold under Agreements to Repurchase	20,700	17,000
Forward Contracts [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Securities Sold under Agreements to Repurchase	$ 9,300	$ 4,500
Weighted Average Forward Start Days | days	16	12
Short-term Debt, Weighted Average Interest Rate, at Point in Time	0.74%	1.60%
Bethesda Securities [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Percentage of Repurchase Agreement Funding	56.00%	40.00%
FICC [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Percentage of Repurchase Agreement Funding	54.00%	38.00%
Obligation to Return Securities Borrowed Under Reverse Repurchase Agreements at Fair Value	$ 4,600	$ 5,400