Debt - Long Term Debt Outstanding (Details)	Dec. 31, 2018 USD ($)	Dec. 31, 2018 EUR (€)	Aug. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2017 EUR (€)	Sep. 30, 2016	Jun. 30, 2015 EUR (€)
Debt Instrument [Line Items]
Total	$ 3,717,000,000			$ 4,249,000,000
Current maturities of long-term debt	0			(500,000,000)
Long-term debt, excluding current maturities	3,717,000,000			3,749,000,000
7.456% Senior Notes Due 2018
Debt Instrument [Line Items]
Total	$ 0			$ 500,000,000
Senior notes, interest rate	7.456%	7.456%	7.456%	7.456%	7.456%
Senior unsecured notes principal amount			$ 500,000,000
5.95% Senior Notes Due 2020
Debt Instrument [Line Items]
Total	$ 748,000,000			$ 748,000,000
Senior notes, interest rate	5.95%	5.95%		5.95%	5.95%	5.95%
Senior unsecured notes principal amount	$ 750,000,000
2.5% Senior Notes Due 2022
Debt Instrument [Line Items]
Total	$ 740,000,000			$ 775,000,000
Senior notes, interest rate	2.50%	2.50%		2.50%	2.50%	2.50%	2.50%
Senior unsecured notes principal amount | €		€ 650,000,000			€ 650,000,000		€ 650,000,000
4.5% Senior Notes Due 2024
Debt Instrument [Line Items]
Total	$ 496,000,000			$ 495,000,000
Senior notes, interest rate	4.50%	4.50%		4.50%	4.50%	4.50%
Senior unsecured notes principal amount	$ 500,000,000
5.0% Senior Notes Due 2026
Debt Instrument [Line Items]
Total	$ 742,000,000			$ 741,000,000
Senior notes, interest rate	5.00%	5.00%		5.00%	5.00%	5.00%
Senior unsecured notes principal amount	$ 750,000,000
3.8% Senior Notes Due 2028
Debt Instrument [Line Items]
Total	$ 991,000,000			$ 990,000,000
Senior notes, interest rate	3.80%	3.80%		3.80%	3.80%
Senior unsecured notes principal amount	$ 1,000,000,000