Incentive Plans - Schedule of Activity Relating to RSUs and DSUs (Detail) - $ / shares	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
RSUs [Member]
Share-based compensation arrangement by share-based payment award [Line Items]
Units, Beginning Balance	12,919,846	11,698,138	9,599,658
Units, Granted	4,245,554	5,437,591	6,878,306
Units, Forfeited	(144,655)	(217,720)	(239,432)
Units, Settled	(5,658,439)	(3,998,163)	(4,540,394)
Units, Ending Balance	11,362,306	12,919,846	11,698,138
Weighted Average Grant Date Fair Value, Beginning Balance	$ 40.23	$ 40.65	$ 44.06
Weighted Average Grant Date Fair Value, Granted	53.44	43.03	34.86
Weighted Average Grant Date Fair Value, Forfeited	44.98	40.20	39.53
Weighted Average Grant Date Fair Value, Settled	42.89	45.26	39.16
Weighted Average Grant Date Fair Value, Ending Balance	$ 43.78	$ 40.23	$ 40.65
DSUs [Member]
Share-based compensation arrangement by share-based payment award [Line Items]
Units, Beginning Balance	278,422	276,725	312,670
Units, Granted	45,124	45,162	48,814
Units, Settled		(43,465)	(84,759)
Units, Ending Balance	323,546	278,422	276,725
Weighted Average Grant Date Fair Value, Beginning Balance	$ 37.46	$ 36.05	$ 35.98
Weighted Average Grant Date Fair Value, Granted	50.40	44.46	35.23
Weighted Average Grant Date Fair Value, Settled		35.77	35.30
Weighted Average Grant Date Fair Value, Ending Balance	$ 39.27	$ 37.46	$ 36.05

The number of equity-based payment instruments, excluding stock (or unit) options, that were forfeited during the reporting period.

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)(iv)(3)
-URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901

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- Definition

Weighted average fair value as of the grant date of equity-based award plans other than stock (unit) option plans that were not exercised or put into effect as a result of the occurrence of a terminating event.

+ 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)(3)
-URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901

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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

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-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

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-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 number of non-vested equity-based payment instruments, excluding stock (or unit) options, that validly exist and are outstanding as of the balance sheet date.

+ References

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
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- Definition

The weighted average fair value of nonvested awards on equity-based plans excluding option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, revenue or profit achievement stock award plan) for which the employer is contingently obligated to issue equity instruments or transfer assets to an employee who has not yet satisfied service or performance criteria necessary to gain title to proceeds from the sale of the award or underlying shares or units.

+ References

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-Publisher FASB
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-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
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- Definition

The number of equity-based payment instruments, excluding stock (or unit) options, that vested during the reporting period.

+ References

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
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- Definition

The weighted average fair value as of grant date pertaining to an equity-based award plan other than a stock (or unit) option plan for which the grantee gained the right during the reporting period, by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash in accordance with the terms of the arrangement.

+ References

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-Publisher FASB
-Name Accounting Standards Codification
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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.

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No definition available.

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