Foreign Exchange Risk Management (Details) € in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019 USD ($)	Jun. 30, 2018 USD ($)	Jun. 30, 2019 USD ($)	Jun. 30, 2018 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2015 EUR (€)
Foreign Exchange Risk Management
Terms of the foreign currency forward contracts and foreign currency option contracts, less than			18 months
Net foreign currency transaction pre-tax loss in AOCI	$ 112		$ 112
Foreign currency derivative contracts
Foreign Exchange Risk Management
Approximate effect of 10% adverse change in foreign currency rates on fair value loss	129		129
General and administrative | Foreign currency derivative contracts
Foreign Exchange Risk Management
Gain (loss) for contracts to purchase and sell foreign currency	(15)	$ 56	(20)	$ 35
Net Investment Hedging
Foreign Exchange Risk Management
Derivative Liability, Notional Amount | €						€ 1,650
Prepaid Expenses and Other Current Assets
Foreign Exchange Risk Management
Foreign Currency Derivative Instruments Not Designated as Hedging Instruments, Asset at Fair Value	$ 12		$ 12		$ 35