Financial and Other Derivative Instruments (Details Textuals) - USD ($)	Jun. 30, 2016	Dec. 31, 2015
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Letters of credit that could be used to offset net derivative liabilities	$ 5,000,000	$ 7,000,000
Letters of credit received that could be used to offset net derivative assets	1,000,000	2,000,000
Cash collateral posted, net of cash collateral received	40,000,000	37,000,000
Collateral adjustment on derivative assets	6,000,000	2,000,000
Collateral adjustment on derivative liabilities	32,000,000	36,000,000
Cash collateral paid	16,000,000	6,000,000
Cash collateral received	2,000,000	$ 3,000,000
Additional collateral, aggregate fair value	322,000,000
Derivative net liability position aggregate fair value	482,000,000
Collateral already posted fair value	0
Derivative net asset position, fair value	425,000,000
Remaining amount of offsets to derivative net liability positions for hard and soft trigger provisions	$ 57,000,000