Financial and Other Derivative Instruments (Details Textuals) - USD ($)	Dec. 31, 2016	Dec. 31, 2015
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Letters of credit that could be used to offset net derivative liabilities	$ 2,000,000	$ 7,000,000
Letters of credit that could be used to offset net derivative assets	2,000,000	2,000,000
Cash collateral posted, net of cash collateral received	34,000,000	37,000,000
Collateral adjustment on derivative assets	7,000,000	2,000,000
Collateral adjustment on derivative liabilities	28,000,000	36,000,000
Cash collateral paid	18,000,000	6,000,000
Cash collateral received	5,000,000	$ 3,000,000
Additional collateral, aggregate fair value	429,000,000
Derivative net liability position aggregate fair value	487,000,000
Collateral already posted fair value	0
Derivative, net asset position, fair value	433,000,000
Remaining amount of offsets to derivative net liability positions for hard and soft trigger provisions	$ 54,000,000