Summary of Significant Accounting Policies (Premises and Equipment) (Details)	12 Months Ended
	Dec. 31, 2017
Buildings | Minimum
Property, Plant and Equipment [Line Items]
Premises and equipment, estimated useful lives	25 years
Buildings | Maximum
Property, Plant and Equipment [Line Items]
Premises and equipment, estimated useful lives	40 years
All other depreciable assets | Minimum
Property, Plant and Equipment [Line Items]
Premises and equipment, estimated useful lives	3 years
All other depreciable assets | Maximum
Property, Plant and Equipment [Line Items]
Premises and equipment, estimated useful lives	10 years