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Stock Option Plans - Stock Options Outstanding and Exercisable (Detail) - $ / shares shares in Millions	9 Months Ended
	Sep. 30, 2018	Dec. 31, 2017
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Range of Exercise Prices, minimum	$ 35.71
Range of Exercise Prices, maximum	$ 70.74
Option Outstanding, Number Outstanding	9.1
Option Outstanding, Weighted Average Remaining Contractual Term (in years)	4 years 18 days
Option Outstanding, Weighted Average Exercise Price	$ 49.93	$ 45.27
Options Exercisable, Number Exercisable	2.3
Option Exercisable, Weighted Average Exercise Price	$ 42.59
Exercise Prices Range $ 35.71 - $ 39.17 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Range of Exercise Prices, minimum	35.71
Range of Exercise Prices, maximum	$ 39.17
Option Outstanding, Number Outstanding	1.1
Option Outstanding, Weighted Average Remaining Contractual Term (in years)	1 year 1 month 20 days
Option Outstanding, Weighted Average Exercise Price	$ 38.08
Options Exercisable, Number Exercisable	1.1
Option Exercisable, Weighted Average Exercise Price	$ 38.08
Exercise Prices Range $ 43.71 - $ 43.71 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Range of Exercise Prices, minimum	43.71
Range of Exercise Prices, maximum	$ 43.71
Option Outstanding, Number Outstanding	2.3
Option Outstanding, Weighted Average Remaining Contractual Term (in years)	4 years 5 months 15 days
Option Outstanding, Weighted Average Exercise Price	$ 43.71
Exercise Prices Range $ 46.17 - $ 46.87 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Range of Exercise Prices, minimum	46.17
Range of Exercise Prices, maximum	$ 46.87
Option Outstanding, Number Outstanding	2.9
Option Outstanding, Weighted Average Remaining Contractual Term (in years)	3 years
Option Outstanding, Weighted Average Exercise Price	$ 46.49
Options Exercisable, Number Exercisable	1.2
Option Exercisable, Weighted Average Exercise Price	$ 46.61
Exercise Prices Range $ 47.92 - $ 63.60 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Range of Exercise Prices, minimum	47.92
Range of Exercise Prices, maximum	$ 63.60
Option Outstanding, Number Outstanding	1.6
Option Outstanding, Weighted Average Remaining Contractual Term (in years)	5 years 5 months 12 days
Option Outstanding, Weighted Average Exercise Price	$ 56.81
Exercise Prices Range $ 70.74 - $ 70.74 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Range of Exercise Prices, minimum	70.74
Range of Exercise Prices, maximum	$ 70.74
Option Outstanding, Number Outstanding	1.2
Option Outstanding, Weighted Average Remaining Contractual Term (in years)	6 years 5 months 15 days
Option Outstanding, Weighted Average Exercise Price	$ 70.74

X

- Definition

Weighted average price at which grantees can acquire the shares reserved for issuance under the stock option 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)(1)(i)
-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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- Definition

The floor of a customized range of exercise prices for purposes of disclosing shares potentially issuable under outstanding stock option awards on all stock option plans and other required information pertaining to awards in the customized range.

+ 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 (g)
-URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901

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- Definition

The number of shares reserved for issuance pertaining to the outstanding exercisable stock options as of the balance sheet date in the customized range of exercise prices for which the market and performance vesting condition has been satisfied.

+ 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)(iii)
-URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901

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- Definition

The number of shares reserved for issuance pertaining to the outstanding stock options as of the balance sheet date for all option plans in the customized range of exercise prices.

+ 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)(1)(i)-(ii)
-URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901

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- Definition

The ceiling of a customized range of exercise prices for purposes of disclosing shares potentially issuable under outstanding stock option awards on all stock option plans and other required information pertaining to awards in the customized range.

+ References

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
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-URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901

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- Definition

Weighted average remaining contractual term for option awards outstanding, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ 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
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- Definition

Weighted average exercise price as of the balance sheet date for those equity-based payment arrangements exercisable and outstanding.

+ References

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-Publisher FASB
-Name Accounting Standards Codification
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-Section 50
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