Fair Value (Carrying Value of Assets Measured at Fair Value on a Non-Recurring Basis) (Details) - USD ($) $ in Millions	Sep. 30, 2017	Dec. 31, 2016
Carrying Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets held for sale	$ 946.2	$ 428.4
Carrying Value | Non-Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Goodwill		51.8
Assets held for sale	141.7	201.6
Other real estate owned	27.3	22.5
Impaired loans	98.3	151.9
Total	267.3	427.8
Estimated Fair Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets held for sale	986.7	439.6
Estimated 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
Estimated Fair Value | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets held for sale	3.5	175.0
Estimated Fair Value | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets held for sale	983.2	264.6
Estimated Fair Value | Non-Recurring | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Goodwill		0.0
Assets held for sale	0.0	0.0
Other real estate owned	0.0	0.0
Impaired loans	0.0	0.0
Total	0.0	0.0
Estimated Fair Value | Non-Recurring | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Goodwill		0.0
Assets held for sale	0.0	0.0
Other real estate owned	0.0	0.0
Impaired loans	0.0	0.0
Total	0.0	0.0
Estimated Fair Value | Non-Recurring | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Goodwill		51.8
Assets held for sale	141.7	201.6
Other real estate owned	27.3	22.5
Impaired loans	98.3	151.9
Total	267.3	427.8
Changes Measurement | Non-Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Goodwill		(354.2)
Assets held for sale	(14.3)	(14.7)
Other real estate owned	(6.3)	(3.2)
Impaired loans	(20.5)	(26.8)
Total	$ (41.1)	$ (398.9)