Income Taxes (Reconciliation Between the Federal Statutory Corporate Tax Rate and the Bancorp's Effective Tax Rate) (Detail)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Reconciliation Of Statutory Federal Tax Rate
Statutory tax rate	35.00%	35.00%	35.00%
State taxes, net of federal benefit	1.60%	1.30%	1.70%
Tax-exempt income	(1.20%)	(2.70%)	(1.70%)
Low-income housing tax credits	(6.00%)	(7.90%)	(6.60%)
Other tax credits	(0.50%)	(0.90%)	(0.90%)
US Tax Legislation Impact On Deferred Taxes	(7.90%)	0.00%	0.00%
Other, net	(0.20%)	(0.40%)	0.30%
Effective tax rate	20.80%	24.40%	27.80%