Leases - Narrative (Details)	3 Months Ended
	Mar. 31, 2019 bank_branch other_office
Lessee, Lease, Description [Line Items]
Number of full-service branch offices related to operating leases | bank_branch	75
Number of other offices related to operating leases | other_office	76
Minimum
Lessee, Lease, Description [Line Items]
Remaining lease term	1 year
Lease renewal term	1 year
Maximum
Lessee, Lease, Description [Line Items]
Remaining lease term	28 years
Lease renewal term	10 years