Fair Value Measurements (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivatives	$ 32	$ 205
Derivatives	109	53
Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities	13	310
Derivatives	32	205
Total assets at fair value	45	515
Derivatives	109	53
Total liabilities at fair value	109	53
Fair Value, Measurements, Recurring [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities	13	310
Derivatives	15	189
Total assets at fair value	28	499
Derivatives	78	47
Total liabilities at fair value	78	47
Fair Value, Measurements, Recurring [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities	0	0
Derivatives	17	16
Total assets at fair value	17	16
Derivatives	31	6
Total liabilities at fair value	31	6
Fair Value, Measurements, Recurring [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities	0	0
Derivatives	0	0
Total assets at fair value	0	0
Derivatives	0	0
Total liabilities at fair value	$ 0	$ 0