Financial and Other Derivative Instruments (Details Textuals) - USD ($)	Dec. 31, 2020	Dec. 31, 2019
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Letters of credit that could be used to offset net derivative liabilities	$ 7,000,000	$ 6,000,000
Letters of credit that could be used to offset net derivative assets	9,000,000	$ 4,000,000
Additional collateral, aggregate fair value	428,000,000
Derivative net liability position aggregate fair value	451,000,000
Collateral already posted fair value	0
Derivative, net asset position, fair value	401,000,000
Remaining amount of offsets to derivative net liability positions for hard and soft trigger provisions	$ 50,000,000