Financial and Other Derivative Instruments (Details Textuals) - USD ($)	Dec. 31, 2015	Dec. 31, 2014
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Letters of credit that could be used to offset net derivative liabilities	$ 7,000,000	$ 7,000,000
Letters of credit received that could be used to offset net derivative assets	2,000,000	5,000,000
Cash collateral posted, net of cash collateral received	37,000,000	61,000,000
Derivative asset, counterparty netting	2,000,000	0
Derivative liability, counterparty netting	36,000,000	19,000,000
Cash collateral paid	6,000,000	44,000,000
Cash collateral received	3,000,000	$ 2,000,000
Additional collateral, aggregate fair value	412,000,000
Derivative net liability position aggregate fair value	592,000,000
Collateral already posted fair value	5,000,000
Derivative, net asset position, fair value	500,000,000
Remaining amount of offsets to derivative net liability positions for hard and soft trigger provisions	$ 87,000,000