Loans (Schedule of Loans by Segment, Based on Obligor Location) (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019	Mar. 31, 2019
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	$ 38,530.4	$ 30,998.9	$ 31,247.0
Commercial Banking
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	30,022.7	24,393.4
Consumer Banking
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	8,507.7	6,605.5
Domestic
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	36,921.9	29,471.5
Domestic | Commercial Banking
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	28,414.2	22,866.0
Domestic | Consumer Banking
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	8,507.7	6,605.5
Foreign
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	1,608.5	1,527.4
Foreign | Commercial Banking
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	$ 1,608.5	$ 1,527.4