Financial Instruments - Fair Value Measurements (Details) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017
Financial assets and financial liabilities measured at fair value on a recurring basis:
Debt securities - current	$ 966	$ 608
Derivative assets	699	942
Derivative liabilities	256	415
Potential reduction in net position of total derivative assets	201	255
Fair value assets, Level 2 to Level 1 transfer	0	0
Fair value assets, Level 1 to Level 2 transfer	0	0
Fair value liabilities, Level 2 to Level 1 transfer	0	0
Fair value liabilities, Level 1 to Level 2 transfer	0	0
Recurring
Financial assets and financial liabilities measured at fair value on a recurring basis:
Cash equivalents	7,599	8,586
Equity investments	10	4
Debt securities - current	963	608
Debt securities - noncurrent		11
Derivative assets	699	942
Total assets	9,270	10,151
Derivative liabilities	256	415
Potential reduction in net position of total derivative assets	201	255
Potential reduction in net position of total derivative liabilities	201	255
Recurring \| Prepaid expenses and other current assets
Financial assets and financial liabilities measured at fair value on a recurring basis:
Derivative assets	301	185
Recurring \| Investments and sundry assets
Financial assets and financial liabilities measured at fair value on a recurring basis:
Derivative assets	398	757
Recurring \| Other accrued expenses and liabilities
Financial assets and financial liabilities measured at fair value on a recurring basis:
Derivative liabilities	94	377
Recurring \| Other liabilities
Financial assets and financial liabilities measured at fair value on a recurring basis:
Derivative liabilities	162	38
Recurring \| Time deposits and certificates of deposit
Financial assets and financial liabilities measured at fair value on a recurring basis:
Cash equivalents	7,123	8,066
Recurring \| Commercial paper
Financial assets and financial liabilities measured at fair value on a recurring basis:
Cash equivalents		96
Recurring \| Money market funds
Financial assets and financial liabilities measured at fair value on a recurring basis:
Cash equivalents	476	26
Recurring \| Canadian government securities
Financial assets and financial liabilities measured at fair value on a recurring basis:
Cash equivalents		398
Recurring \| Level 1
Financial assets and financial liabilities measured at fair value on a recurring basis:
Cash equivalents	476	26
Equity investments	10	4
Debt securities - noncurrent		4
Total assets	485	33
Recurring \| Level 1 \| Money market funds
Financial assets and financial liabilities measured at fair value on a recurring basis:
Cash equivalents	476	26
Recurring \| Level 2
Financial assets and financial liabilities measured at fair value on a recurring basis:
Cash equivalents	7,123	8,560
Debt securities - current	963	608
Debt securities - noncurrent		7
Derivative assets	699	942
Total assets	8,785	10,117
Derivative liabilities	256	415
Recurring \| Level 2 \| Time deposits and certificates of deposit
Financial assets and financial liabilities measured at fair value on a recurring basis:
Cash equivalents	$ 7,123	8,066
Recurring \| Level 2 \| Commercial paper
Financial assets and financial liabilities measured at fair value on a recurring basis:
Cash equivalents		96
Recurring \| Level 2 \| Canadian government securities
Financial assets and financial liabilities measured at fair value on a recurring basis:
Cash equivalents		$ 398

Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

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Fair value portion of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

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Fair value of financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset, elected not to be offset, deducted from derivative assets.

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Fair value of financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset, elected not to be offset, deducted from derivative liabilities.

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Amount of investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI).

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Amount of transfers of assets measured on a recurring basis out of Level 1 of the fair value hierarchy into Level 2.

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