Contingencies (Details) (USD $) In Millions, unless otherwise specified						6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013 Standby Letters of Credit [Member]	Jun. 30, 2012 Standby Letters of Credit [Member]	Jun. 30, 2013 Pending or Threatened Litigation, Stanford Financial Group [Member] Lawsuit	Jun. 30, 2013 Pending or Threatened Litigation, Overdraft Fees [Member] Member Lawsuit
Loss Contingencies [Line Items]
Unused commitments to extend credit	$ 1,963	$ 1,663
Maximum potential exposure to credit loss in the event of nonperformance			164.0	157.1
Letters of credit, maturity term - maximum			3
Collateral held, fair value			51.3
Legal Proceedings [Abstract]
Lawsuits naming entity as defendant, number					2	2
Minimum number of settlement class members to opt out of settlement for termination of settlement to occur						100
Gross settlement						4
Litigation settlement net						$ 2.5