Share-Based Payments - Narrative (Detail)	12 Months Ended
Dec. 31, 2017 shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares available for award	290,000,000
2014 Stock Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of additional shares authorized	520,000,000
Maximum shares available per individual during the plan period	20,000,000
2004 Stock Plan, Amended and Restated [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum shares available per individual during the plan period	8,000,000
Restricted Stock Units (RSUs) [Member] \| 2014 Stock Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares counted toward maximum	3
Restricted Stock Units (RSUs) [Member] \| 2004 Stock Plan, Amended and Restated [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares counted toward maximum	2
Portfolio Performance Shares [Member] \| 2014 Stock Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares counted toward maximum	3
Performance Shares [Member] \| 2014 Stock Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares counted toward maximum	3
Total Shareholder Return Units (TSRUs) [Member] \| 2004 Stock Plan, Amended and Restated [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares counted toward maximum	1
Performance Total Shareholder Return Unit (PTSRUs) [Member] \| 2004 Stock Plan, Amended and Restated [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares counted toward maximum	1
Employee Stock Option [Member] \| 2004 Stock Plan, Amended and Restated [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares counted toward maximum	1

Share Based Compensation Arrangement By Share Based Payment Award, Maximum Number of Awards Granted Per Employee

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- Definition

Share Based Compensation Arrangement By Share Based Payment Award, Shares Counted Toward Maximum Number of Awards Granted Per Employee

+ References

No definition available.

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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

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- Definition

Number of additional shares authorized for issuance under an established share-based compensation plan.

+ References

No definition available.

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- Definition

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.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901

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