Fair Value Measurements (Details) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017	Jun. 30, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Abstract]
Derivatives	$ 16	$ 22
Derivatives	84	$ 124
Recurring Basis
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Abstract]
Marketable Securities	60		$ 9
Derivatives	16		22
Total Assets at Fair Value	76		31
Derivatives	84		124
Total Liabilities at Fair Value	84		124
Recurring Basis | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Abstract]
Marketable Securities	60		9
Derivatives	1		0
Total Assets at Fair Value	61		9
Derivatives	52		78
Total Liabilities at Fair Value	52		78
Recurring Basis | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Abstract]
Marketable Securities	0		0
Derivatives	15		22
Total Assets at Fair Value	15		22
Derivatives	32		46
Total Liabilities at Fair Value	32		46
Recurring Basis | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Abstract]
Marketable Securities	0		0
Derivatives	0		0
Total Assets at Fair Value	0		0
Derivatives	0		0
Total Liabilities at Fair Value	$ 0		$ 0