Derivative Instruments and Hedging Activities Interest Spread on Interest Rate Swaps (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Derivative Instruments, Gain (Loss) [Line Items]
Derivative, Average Notional Amount	$ 24,908,389	$ 28,369,326	$ 23,741,682	$ 34,416,325
Interest Rate Swap [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Interest Expense on Interest Rate Swap and Swaption Agreements	(7,656)	(26,147)	(13,846)	(53,673)
Derivative, Average Notional Amount	$ 14,806,049	$ 16,681,983	$ 14,880,324	$ 17,455,887