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Fair Value Measurements (Details Textuals) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Fair Value of Financial Instruments [Line Items]
Investment excludes receivables, payables and accrued income	$ (15)	$ (11)
Cash balance excluded from available for sale securities		11
Investments not required to be disclosed	$ 252	$ 255
NUG contracts
Fair Value of Financial Instruments [Line Items]
Period of future observable data to determine contract price	2 years

X

- Definition

Cash receivables payables deferred taxes accrued income balance excluded from available for sale securities.

+ References

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- Definition

Derivative, Contract Price, Period of Future Observable Data

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X

- Definition

Fair Value of Financial Instruments.

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- Definition

Investments excludes receivables payables deferred taxes and accrued income.

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- Definition

Investments not required to be disclosed.

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- Details

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