Pledged and Restricted Assets (Type of Pledged Assets) (Details) - USD ($) $ in Billions	Mar. 31, 2021	Dec. 31, 2020
Financial Instruments Owned and Pledged as Collateral [Line Items]
Total Pledged Assets	$ 45.9	$ 47.5
Obligations of States and Political Subdivisions
Financial Instruments Owned and Pledged as Collateral [Line Items]
Total Pledged Assets	3.0	2.9
Government Sponsored Agency and Other Securities
Financial Instruments Owned and Pledged as Collateral [Line Items]
Total Pledged Assets	30.6	32.5
Loans
Financial Instruments Owned and Pledged as Collateral [Line Items]
Total Pledged Assets	$ 12.3	$ 12.1