Financial and Other Derivative Instruments (Details Textuals) (USD $)	Dec. 31, 2014	Dec. 31, 2013
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Letters of credit that could be used to offset net derivative liabilities	$ 7,000,000	$ 19,000,000
Letters of credit received that could be used to offset net derivative assets	5,000,000	1,000,000
Cash collateral posted, net of cash collateral received	61,000,000	12,000,000
Derivative asset, counterparty netting	0	26,000,000
Derivative liability, counterparty netting	19,000,000	17,000,000
Cash collateral received	2,000,000	13,000,000
Cash collateral paid	44,000,000	34,000,000
Derivative net liability position aggregate fair value	1,058,000,000
Collateral already posted fair value	12,000,000
Derivative, net asset position, fair value	973,000,000
Remaining amount of offsets to derivative net liability positions for hard and soft trigger provisions	73,000,000
Additional collateral, aggregate fair value	$ 349,000,000