Pledged Assets (Narrative) (Details) - USD ($)	3 Months Ended	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Financial Instruments Owned and Pledged as Collateral [Line Items]
Security owned and pledged as collateral, fair value		$ 43,400,000,000		$ 42,100,000,000
Securities eligible to be repledged or sold		268,600,000		487,200,000
Collateral securities repledged, delivered, or used		0		0
Average deposits maintained to meet Federal Reserve Bank reserve requirements	$ 1,600,000,000	500,000,000	$ 1,500,000,000
Collateral Requirements
Financial Instruments Owned and Pledged as Collateral [Line Items]
Security owned and pledged as collateral, fair value		$ 7,600,000,000		$ 8,500,000,000