Balance Sheet Offsetting Balance Sheet Offsetting (Narrative) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2013	Mar. 31, 2014 Swaps with Central Clearing Agency [Member]	Mar. 31, 2014 Collateral Swap [Member]	Mar. 31, 2014 Investment Securities [Member] Swaps with Central Clearing Agency [Member]	Mar. 31, 2014 Cash [Member] Swaps with Central Clearing Agency [Member]
Balance Sheet Offsetting [Line Items]
Swap Net Liability Position Fair Value		$ 9.5
Value Of Collateral Posted				9.8	2.3
Collateral Already Posted, Aggregate Fair Value			310.2
Collateral Swap Agreements	300.0		300.0
Collateral Accepted, Aggregate Fair Value			$ 330.6