Debt and Credit Facilities - Summary of Debt Carrying Amount (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017
Debt Instrument [Line Items]
Less current portion	$ 2,748	$ 2,747
Total long-term debt, net	$ 24,574	30,795
Term Loan Facilities
Debt Instrument [Line Items]
Interest Rate	1.85%
Term Loan Facilities \| Term Loan Due October 2018
Debt Instrument [Line Items]
Long-term debt	$ 0	999
Term Loan Facilities \| Term Loan Due October 2020
Debt Instrument [Line Items]
Long-term debt	0	998
Term Loan Facilities \| Term Loan Due October 2022
Debt Instrument [Line Items]
Long-term debt	$ 0	2,497
Unsecured Debt \| Senior Unsecured Notes Due in September 2018
Debt Instrument [Line Items]
Interest Rate	1.85%
Long-term debt	$ 0	999
Unsecured Debt \| 2017 Senior Unsecured Notes Due in September 2018
Debt Instrument [Line Items]
Long-term debt	0	749
Unsecured Debt \| 2017 Senior Unsecured Notes Due in March 2019
Debt Instrument [Line Items]
Long-term debt	$ 750	748
Unsecured Debt \| Senior Unsecured Notes Due in April 2019
Debt Instrument [Line Items]
Interest Rate	2.05%
Long-term debt	$ 500	499
Unsecured Debt \| 2017 Senior Unsecured Notes Due in September 2019 with Fixed Rate
Debt Instrument [Line Items]
Interest Rate	1.85%
Long-term debt	$ 999	997
Unsecured Debt \| 2017 Senior Unsecured Notes Due in September 2019 with Floating Rate
Debt Instrument [Line Items]
Long-term debt	$ 499	499
Unsecured Debt \| Senior Unsecured Notes Due In February 2020
Debt Instrument [Line Items]
Interest Rate	2.35%
Long-term debt	$ 499	499
Unsecured Debt \| Senior Unsecured Notes Due in September 2020
Debt Instrument [Line Items]
Interest Rate	2.55%
Long-term debt	$ 1,996	1,994
Unsecured Debt \| Senior Unsecured Notes Due in April 2021
Debt Instrument [Line Items]
Interest Rate	4.50%
Long-term debt	$ 997	995
Unsecured Debt \| Senior Unsecured Notes Due In December 2021
Debt Instrument [Line Items]
Interest Rate	4.40%
Long-term debt	$ 1,247	1,246
Unsecured Debt \| Senior Unsecured Notes Due in March 2022
Debt Instrument [Line Items]
Interest Rate	1.95%
Long-term debt	$ 498	497
Unsecured Debt \| Senior Unsecured Notes Due in September 2022
Debt Instrument [Line Items]
Interest Rate	3.25%
Long-term debt	$ 997	996
Unsecured Debt \| Senior Unsecured Notes Due in September 2023
Debt Instrument [Line Items]
Interest Rate	2.50%
Long-term debt	$ 746	745
Unsecured Debt \| Senior Unsecured Notes Due in April 2024
Debt Instrument [Line Items]
Interest Rate	3.70%
Long-term debt	$ 1,744	1,742
Unsecured Debt \| Senior Unsecured Notes Due in February 2025
Debt Instrument [Line Items]
Interest Rate	3.50%
Long-term debt	$ 1,745	1,744
Unsecured Debt \| Senior Unsecured Notes Due in March 2026
Debt Instrument [Line Items]
Interest Rate	3.65%
Long-term debt	$ 2,731	2,729
Unsecured Debt \| Senior Unsecured Notes Due in March 2027
Debt Instrument [Line Items]
Interest Rate	2.95%
Long-term debt	$ 1,245	1,244
Unsecured Debt \| Senior Unsecured Notes Due in September 2035
Debt Instrument [Line Items]
Interest Rate	4.60%
Long-term debt	$ 990	990
Unsecured Debt \| Senior Unsecured Notes Due in September 2036
Debt Instrument [Line Items]
Interest Rate	4.00%
Long-term debt	$ 740	740
Unsecured Debt \| Senior Unsecured Notes Due in December 2041
Debt Instrument [Line Items]
Interest Rate	5.65%
Long-term debt	$ 995	995
Unsecured Debt \| Senior Unsecured Notes Due in April 2044
Debt Instrument [Line Items]
Interest Rate	4.80%
Long-term debt	$ 1,734	1,733
Unsecured Debt \| Senior Unsecured Notes Due in February 2045
Debt Instrument [Line Items]
Interest Rate	4.50%
Long-term debt	$ 1,730	1,730
Unsecured Debt \| Senior Unsecured Notes Due in March 2046
Debt Instrument [Line Items]
Interest Rate	4.75%
Long-term debt	$ 2,216	2,215
Unsecured Debt \| Senior Unsecured Notes Due in March 2047
Debt Instrument [Line Items]
Interest Rate	4.15%
Long-term debt	$ 1,724	$ 1,723
London Interbank Offered Rate (LIBOR) \| 2017 Senior Unsecured Notes Due in September 2019 with Floating Rate
Debt Instrument [Line Items]
Basis Spread	0.25%
London Interbank Offered Rate (LIBOR) \| 2017 Senior Unsecured Notes Due in March 2019
Debt Instrument [Line Items]
Basis Spread	0.22%
London Interbank Offered Rate (LIBOR) \| 2017 Senior Unsecured Notes Due in September 2018
Debt Instrument [Line Items]
Basis Spread	0.17%

Percentage points added to the reference rate to compute the variable rate on the debt instrument.

No definition available.

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- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

+ References

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

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- Definition

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/disclosureRef
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- Definition

Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt, classified as current. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
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-Topic 210
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- Definition

Amount after unamortized (discount) premium and debt issuance costs of long-term debt classified as noncurrent and excluding amounts to be repaid within one year or the normal operating cycle, if longer. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

+ References

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