| Derivative Instruments and Hedging Activities Interest Spread on Interest Rate Swaps (Details) - USD ($) $ in Thousands | 3 Months Ended | |
|---|---|---|
| Mar. 31, 2016 | Mar. 31, 2015 | |
| Derivative Instruments, Gain (Loss) [Line Items] | ||
| Derivative, Average Notional Amount | $ 22,574,979 | $ 42,996,135 | 
| Interest Rate Swap [Member] | ||
| Derivative Instruments, Gain (Loss) [Line Items] | ||
| Interest Expense on Interest Rate Swap and Swaption Agreements | (6,190) | (27,525) | 
| Derivative, Average Notional Amount | $ 14,954,600 | $ 18,238,389 | 
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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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