Derivative Instruments and Hedging Activities Interest Spread on Interest Rate Swaps (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Derivative Instruments, Gain (Loss) [Line Items]
Derivative, Average Notional Amount	$ 21,641,836	$ 29,925,251
Interest Rate Swap [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Interest Expense on Interest Rate Swap and Swaption Agreements	(21,074)	(85,636)	$ (91,754)
Derivative, Average Notional Amount	$ 15,506,763	$ 16,091,714	$ 23,329,504