Financial Instruments, Hedging Activities and Fair Value Measurements (Additional Information) (Details) € in Billions	6 Months Ended		12 Months Ended
	Jun. 30, 2018 USD ($)	Jun. 30, 2018 EUR (€)	Dec. 31, 2017 EUR (€)	Dec. 31, 2016 USD ($)	Feb. 28, 2018 USD ($)	Dec. 31, 2017 USD ($)
Derivative Instruments and Hedging Activities Disclosure [Line Items]
Notional amount	$ 560,000,000
Fair Value of Debt Instrument Designated as a Hedge of Net Investment in Foreign Operations						$ 2,700,000,000
Accumulated pretax unrealized translation gains (losses) in AOCI, related to both the euro-denominated borrowings and the cross currency swaps that have been designated as hedges of net investments	95,000,000			$ 16,000,000
Capital Lease Obligations	14,000,000					15,000,000
Short-term Debt	18,000,000					8,000,000
Long-term Debt	5,038,000,000					4,123,000,000
Long-lived assets fair value amount	$ 5,204,000,000					$ 4,341,000,000
Interest Rate Swap [Member]
Derivative Instruments and Hedging Activities Disclosure [Line Items]
Notional amount					$ 525,000,000
Currency Swap [Member]
Derivative Instruments and Hedging Activities Disclosure [Line Items]
Notional amount					$ 575,000,000
Net Investment Hedging [Member]
Derivative Instruments and Hedging Activities Disclosure [Line Items]
Long-term Debt | €		€ 2.3	€ 2.3