Fair Value Measurements - Summary of Activity Related to Equity Investments (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2018	Dec. 31, 2017
Equity Investment [Roll Forward]
Non Current Other Assets	$ 4,465	$ 4,971
Equity Securities | Equity Investments with readily determinable value
Equity Investment [Roll Forward]
Carrying value, beginning of period	751
Changes in Fair Value Reflected in Net Income	(35)
Sales/ Purchases/Other	(19)
Carrying value, end of period	697
Non Current Other Assets	697
Equity Securities | Equity Investments without readily determinable value
Equity Investment [Roll Forward]
Carrying value, beginning of period	510
Changes in Fair Value Reflected in Net Income	7
Sales/ Purchases/Other	122
Carrying value, end of period	639
Non Current Other Assets	$ 639