Pledged and Restricted Assets (Type of Pledged Assets) (Details) - USD ($) $ in Billions	Sep. 30, 2021	Dec. 31, 2020
Financial Instruments Owned and Pledged as Collateral [Line Items]
Total Pledged Assets	$ 54.8	$ 47.5
Obligations of States and Political Subdivisions
Financial Instruments Owned and Pledged as Collateral [Line Items]
Total Pledged Assets	3.6	2.9
Government Sponsored Agency and Other Securities
Financial Instruments Owned and Pledged as Collateral [Line Items]
Total Pledged Assets	35.5	32.5
Loans
Financial Instruments Owned and Pledged as Collateral [Line Items]
Total Pledged Assets	$ 15.7	$ 12.1