Derivative Instruments and Hedging Activities Interest Spread on Interest Rate Swaps (Details) - USD ($) $ in Thousands  | 
3 Months Ended | 6 Months Ended | ||
|---|---|---|---|---|
Jun. 30, 2015  | 
Jun. 30, 2014  | 
Jun. 30, 2015  | 
Jun. 30, 2014  | 
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| Derivative Instruments, Gain (Loss) [Line Items] | ||||
| Derivative, Average Notional Amount | $ 28,369,326 | $ 43,273,172 | $ 34,416,325 | $ 42,023,975 | 
| Interest Rate Swap [Member] | ||||
| Derivative Instruments, Gain (Loss) [Line Items] | ||||
| Interest Expense on Interest Rate Swap and Swaption Agreements | (26,147) | (18,891) | (53,673) | (32,727) | 
| Derivative, Average Notional Amount | $ 16,681,983 | $ 23,467,489 | $ 17,455,887 | $ 21,324,091 | 
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- Definition Average notional amount during the period presented specified by the derivative(s). No definition available. 
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- Definition Net interest spread on interest rate swap and swaption agreements, at fair value. No definition available. 
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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. No definition available. 
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- Details 
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