Quarterly report pursuant to Section 13 or 15(d)

Derivative Instruments and Hedging Activities Credit Risk - Counterparty Exposure (Details)

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Derivative Instruments and Hedging Activities Credit Risk - Counterparty Exposure (Details) (USD $)
In Millions, unless otherwise specified
Mar. 31, 2012
Credit Derivatives [Line Items]  
Collateral Securities Repledged, Delivered, or Used $ (55.6)
Collateral Already Posted, Aggregate Fair Value $ 101.8