Stock-Based Compensation - Narrative (Details) $ / shares in Units, shares in Millions, $ in Millions	9 Months Ended
Sep. 30, 2018 USD ($) $ / shares shares
Employee stock option
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock granted in period (shares) \| shares	0.2
Weighted-average grant date fair value of stock granted in period (USD per share) \| $ / shares	$ 128.46
Unrecognized compensation expense \| $	$ 3
Unrecognized compensation expense, period for recognition	2 years 3 months 1 day
Restricted stock and unit awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock granted in period (shares) \| shares	0.7
Weighted-average grant date fair value of stock granted in period (USD per share) \| $ / shares	$ 170.44
Unrecognized compensation expense \| $	$ 99
Unrecognized compensation expense, period for recognition	2 years 1 month

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.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (i)
-URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901

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- Definition

Unrecognized cost of unvested share-based awards, other than options, awarded to employees as compensation.

+ References

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- Definition

The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(2)(iii)(1)
-URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901

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- Definition

The weighted average fair value at grant date for nonvested equity-based awards issued during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(2)(iii)(1)
-URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901

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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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