Loans (Loans - Delinquency Status) (Parenthetical) (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019	Mar. 31, 2019
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans (see Note 9 for amounts pledged)	$ 38,530.4	$ 30,998.9	$ 31,247.0
Total past due	608.6	417.3
90 days or more past due loans	18.9	36.9
90 or more Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	157.0	96.3
PCD Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans (see Note 9 for amounts pledged)	1,600.0
PCD Loans | 90 or more Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
90 days or more past due loans	44.0
Consumer Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans (see Note 9 for amounts pledged)	7,833.6	5,979.4
90 days or more past due loans	11.5	$ 11.3
Consumer Loans | Legacy Consumer Mortgages | PCD Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	$ 172.6