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Debt and Credit Facilities - Summary of Debt Carrying Amount (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Debt Instrument [Line Items]
Total debt, net	$ 29,054	$ 33,542
Less current portion	2,497	2,747
Total long-term debt, net	$ 26,557	30,795
Senior Unsecured Notes Due in September 2018
Debt Instrument [Line Items]
Interest Rate	1.85%
Senior unsecured notes	$ 999	999
2017 Senior Unsecured Notes Due in September 2018
Debt Instrument [Line Items]
Senior unsecured notes	$ 749	749
Basis Spread	0.17%
Variable Rate Basis	3-month LIBOR
2017 Senior Unsecured Notes Due in March 2019
Debt Instrument [Line Items]
Senior unsecured notes	$ 749	748
Basis Spread	0.22%
Variable Rate Basis	3-month LIBOR
Senior Unsecured Notes Due in April 2019
Debt Instrument [Line Items]
Interest Rate	2.05%
Senior unsecured notes	$ 499	499
2017 Senior Unsecured Notes Due in September 2019 with Fixed Rate
Debt Instrument [Line Items]
Interest Rate	1.85%
Senior unsecured notes	$ 997	997
2017 Senior Unsecured Notes Due in September 2019 with Floating Rate
Debt Instrument [Line Items]
Senior unsecured notes	$ 499	499
Basis Spread	0.25%
Variable Rate Basis	3-month LIBOR
Senior Unsecured Notes Due In February 2020
Debt Instrument [Line Items]
Interest Rate	2.35%
Senior unsecured notes	$ 499	499
Senior Unsecured Notes Due in September 2020
Debt Instrument [Line Items]
Interest Rate	2.55%
Senior unsecured notes	$ 1,994	1,994
Term Loan Due October 2020
Debt Instrument [Line Items]
Long-term Line of Credit	$ 0	998
Senior Unsecured Notes Due in April 2021
Debt Instrument [Line Items]
Interest Rate	4.50%
Senior unsecured notes	$ 996	995
Senior Unsecured Notes Due In December 2021
Debt Instrument [Line Items]
Interest Rate	4.40%
Senior unsecured notes	$ 1,247	1,246
Senior Unsecured Notes Due in March 2022
Debt Instrument [Line Items]
Interest Rate	1.95%
Senior unsecured notes	$ 498	497
Senior Unsecured Notes Due in September 2022
Debt Instrument [Line Items]
Interest Rate	3.25%
Senior unsecured notes	$ 996	996
Term Loan Due October 2022 [Member]
Debt Instrument [Line Items]
Long-term Line of Credit	$ 0	2,497
Senior Unsecured Notes Due in September 2023
Debt Instrument [Line Items]
Interest Rate	2.50%
Senior unsecured notes	$ 745	745
Senior Unsecured Notes Due in April 2024
Debt Instrument [Line Items]
Interest Rate	3.70%
Senior unsecured notes	$ 1,743	1,742
Senior Unsecured Notes Due in February 2025
Debt Instrument [Line Items]
Interest Rate	3.50%
Senior unsecured notes	$ 1,744	1,744
Senior Unsecured Notes Due in March 2026
Debt Instrument [Line Items]
Interest Rate	3.65%
Senior unsecured notes	$ 2,729	2,729
Senior Unsecured Notes Due in March 2027
Debt Instrument [Line Items]
Interest Rate	2.95%
Senior unsecured notes	$ 1,244	1,244
Senior Unsecured Notes Due in September 2035
Debt Instrument [Line Items]
Interest Rate	4.60%
Senior unsecured notes	$ 990	990
Senior Unsecured Notes Due in September 2036
Debt Instrument [Line Items]
Interest Rate	4.00%
Senior unsecured notes	$ 740	740
Senior Unsecured Notes Due in December 2041
Debt Instrument [Line Items]
Interest Rate	5.65%
Senior unsecured notes	$ 995	995
Senior Unsecured Notes Due in April 2044
Debt Instrument [Line Items]
Interest Rate	4.80%
Senior unsecured notes	$ 1,733	1,733
Senior Unsecured Notes Due in February 2045
Debt Instrument [Line Items]
Interest Rate	4.50%
Senior unsecured notes	$ 1,730	1,730
Senior Unsecured Notes Due in March 2046
Debt Instrument [Line Items]
Interest Rate	4.75%
Senior unsecured notes	$ 2,215	2,215
Senior Unsecured Notes Due in March 2047
Debt Instrument [Line Items]
Interest Rate	4.15%
Senior unsecured notes	$ 1,724	1,723
Term Loan Due October 2018
Debt Instrument [Line Items]
Line of Credit, Current	$ 0	$ 999

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

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The reference rate for the variable rate of the debt instrument, such as LIBOR or the US Treasury rate and the maturity of the reference rate used, such as three months or six months LIBOR.

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

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The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

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