Share-Based Compensation Plans - Narrative (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Shares collectively authorized for future grants under share-based compensation plans (in shares)	118,000,000
Quantity of stock options that vest per year (as percent)	33.33%
Period over which share-based payment awards vest	3 years
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Pretax share-based compensation cost	$ 312	$ 300	$ 299
Income tax benefits related to share-based compensation	$ 57	$ 92	$ 93
Weighted average exercise price of options granted (in dollars per share)	$ 63.88	$ 54.63	$ 59.73
Weighted average fair value of options granted (in dollars per share)	$ 7.04	$ 5.89	$ 6.46
Total pre tax unrecognized compensation expense related to nonvested stock options, RSU and PSU awards	$ 469
Weighted average period in years of recognition for nonvested stock options, RSU and PSU awards	1 year 10 months 25 days
Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Contractual term of options	7 years
Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Contractual term of options	10 years

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Unrecognized cost of unvested share-based compensation awards.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (i)
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Weighted average period over which unrecognized compensation is expected to be recognized for equity-based compensation plans, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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The total recognized tax benefit related to compensation cost for equity-based payment arrangements recognized in income during the period.

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-Publisher FASB
-Name Accounting Standards Codification
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The aggregate amount of noncash, equity-based employee remuneration. This may include the value of stock or unit options, amortization of restricted stock or units, and adjustment for officers' compensation. As noncash, this element is an add back when calculating net cash generated by operating activities using the indirect method.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
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-Section 45
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Estimated period over which an employee is required to provide service in exchange for the equity-based payment award, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
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Period which an employee's right to exercise an award is no longer contingent on satisfaction of either a service condition, market condition or a performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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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.

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The difference between the maximum number of shares (or other type of equity) authorized for issuance under the plan (including the effects of amendments and adjustments), and the sum of: 1) the number of shares (or other type of equity) already issued upon exercise of options or other equity-based awards under the plan; and 2) shares (or other type of equity) reserved for issuance on granting of outstanding awards, net of cancellations and forfeitures, if applicable.

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The weighted average grant-date fair value of options granted during the reporting period as calculated by applying the disclosed option pricing methodology.

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Weighted average per share amount at which grantees can acquire shares of common stock by exercise of options.

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Percentage of vesting of share-based compensation awards.

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