Fair Value (Carrying Value of Assets Measured at Fair Value on a Non-Recurring Basis) (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Carrying Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets held for sale	$ 49.2	$ 29.6
Carrying Value | Non-Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets held for sale	27.1	22.6
Collateral-dependent loans	12.8
Impaired loans		244.8
Tax credit investments	0.0	82.0
Mortgage Servicing Rights	7.8
Total Assets	47.7	349.4
Fair Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets held for sale	49.4	29.7
Fair Value | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets held for sale	0.0	0.0
Fair Value | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets held for sale	21.3	7.5
Fair Value | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets held for sale	28.1	22.2
Fair Value | Non-Recurring | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets held for sale	0.0	0.0
Collateral-dependent loans	0.0
Impaired loans		0.0
Tax credit investments	0.0	0.0
Mortgage Servicing Rights	0.0
Total Assets	0.0	0.0
Fair Value | Non-Recurring | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets held for sale	2.7	1.9
Collateral-dependent loans	0.0
Impaired loans		0.0
Tax credit investments	0.0	0.0
Mortgage Servicing Rights	0.0
Total Assets	2.7	1.9
Fair Value | Non-Recurring | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets held for sale	24.4	20.7
Collateral-dependent loans	12.8
Impaired loans		244.8
Tax credit investments	0.0	82.0
Mortgage Servicing Rights	7.8
Total Assets	45.0	347.5
Total Gains (Losses) | Non-Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets held for sale	(4.0)	2.2
Collateral-dependent loans	(26.6)
Impaired loans		(73.5)
Tax credit investments	0.0	(5.1)
Mortgage Servicing Rights	(2.0)
Total Assets	$ (32.6)	$ (76.4)