Balance Sheet Offsetting Balance Sheet Offsetting (Narrative) (Details) (USD $) In Millions, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Swaps with Central Clearing Agency [Member]
Balance Sheet Offsetting [Line Items]
Swap Net Liability Position Fair Value	$ 11.7
Collateral Swap [Member]
Balance Sheet Offsetting [Line Items]
Collateral Already Posted, Aggregate Fair Value	411.8
Collateral Swap Agreements	400.0	300.0
Collateral Accepted, Aggregate Fair Value	438.4
Investment Securities [Member] | Swaps with Central Clearing Agency [Member]
Balance Sheet Offsetting [Line Items]
Value Of Collateral Posted	8.1
Cash [Member] | Swaps with Central Clearing Agency [Member]
Balance Sheet Offsetting [Line Items]
Value Of Collateral Posted	$ 4.6