Debt - Long Term Debt Outstanding (Details)	Jun. 30, 2018 EUR (€)	Jun. 30, 2018 USD ($)	Dec. 31, 2017 USD ($)
Debt Instrument [Line Items]
Total debt		$ 4,231,000,000	$ 4,249,000,000
Current maturities of long-term debt		(500,000,000)	(500,000,000)
Long-term debt, excluding current maturities		3,731,000,000	3,749,000,000
7.456% Senior Notes Due 2018
Debt Instrument [Line Items]
Total debt		$ 500,000,000	500,000,000
Debt, interest rate (percentage)	7.456%	7.456%
Senior unsecured notes principal amount		$ 500,000,000
5.95% Senior Notes Due 2020
Debt Instrument [Line Items]
Total debt		$ 748,000,000	748,000,000
Debt, interest rate (percentage)	5.95%	5.95%
Senior unsecured notes principal amount		$ 750,000,000
2.5% Senior Notes Due 2022
Debt Instrument [Line Items]
Total debt		$ 755,000,000	775,000,000
Debt, interest rate (percentage)	2.50%	2.50%
Senior unsecured notes principal amount \| €	€ 650,000,000
4.5% Senior Notes Due 2024
Debt Instrument [Line Items]
Total debt		$ 496,000,000	495,000,000
Debt, interest rate (percentage)	4.50%	4.50%
Senior unsecured notes principal amount		$ 500,000,000
5.0% Senior Notes Due 2026
Debt Instrument [Line Items]
Total debt		$ 742,000,000	741,000,000
Debt, interest rate (percentage)	5.00%	5.00%
Senior unsecured notes principal amount		$ 750,000,000
3.8% senior notes due 2028
Debt Instrument [Line Items]
Total debt		$ 990,000,000	$ 990,000,000
Debt, interest rate (percentage)	3.80%	3.80%
Senior unsecured notes principal amount		$ 1,000,000,000

Face (par) amount of debt instrument at time of issuance.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 55
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=64930739&loc=d3e28878-108400

Reference 2: http://www.xbrl.org/2003/role/presentationRef
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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22(a)(1))
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Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(a)(16))
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