Fair Value Measurements (Details Textuals) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment excludes receivables, payables and accrued income	$ 4	$ (11)
Cash balance excluded from available for sale securities	20	11
Investments not required to be disclosed	$ 253	$ 255
NUG contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Period of future observable data to determine contract price	2 years