Contingencies (Details) (USD $) In Millions, unless otherwise specified			3 Months Ended			1 Months Ended	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013	Mar. 31, 2014 Standby Letters of Credit [Member]	Mar. 31, 2013 Standby Letters of Credit [Member]	Mar. 31, 2014 Pending or Threatened Litigation, Stanford Financial Group [Member] Lawsuit	Oct. 31, 2013 Pending or Threatened Litigation, Overdraft Fees [Member] Member	Jun. 30, 2013 Pending or Threatened Litigation, Overdraft Fees [Member]	Mar. 31, 2014 Pending or Threatened Litigation, Overdraft Fees [Member] Lawsuit	Oct. 25, 2013 Pending or Threatened Litigation, Overdraft Fees [Member]
Loss Contingencies [Line Items]
Unused commitments to extend credit	$ 2,289	$ 2,091
Maximum potential exposure to credit loss in the event of nonperformance			147.2	156.1
Letters of credit, maturity term - maximum			3 years
Collateral held, fair value			37.0
Legal Proceedings [Abstract]
Lawsuits naming entity as defendant, number					2			2
Number of class member opted out of settlement, maximum						20
Litigation settlement							4.0
Litigation settlement net of taxes							2.5
Settlement amount deposited into Settlement Administrator escrow account									$ 4.0