Pledged Assets (Narrative) (Details) - USD ($)	3 Months Ended	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Financial Instruments Owned and Pledged as Collateral [Line Items]
Total Pledged Assets		$ 43,800,000,000		$ 42,100,000,000
Securities eligible to be repledged or sold		35,000,000.0		487,200,000
Collateral securities repledged, delivered, or used		0		0
Average deposits maintained to meet Federal Reserve Bank reserve requirements	$ 1,500,000,000	800,000,000	$ 1,500,000,000
Collateral Requirements
Financial Instruments Owned and Pledged as Collateral [Line Items]
Total Pledged Assets		$ 9,000,000,000.0		$ 8,500,000,000