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Equity-Based Compensation (Summary of Phantom Unit Award Activity) (Detail) - Phantom Units - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Number of Units
Outstanding at December 31, 2017	1,351,523
Granted	437,092
Settled	(509,570)
Forfeited	(124,710)
Outstanding at December 31, 2018	1,154,335	1,351,523
Vested and expected to vest at December 31, 2018	1,139,877
Non-forfeitable at December 31, 2018(1)	321,638
Weighted Average Fair Value
Outstanding at December 31, 2016 (usd per share)	$ 34.53
Granted (usd per share)	33.84	$ 36.26	$ 29.42
Settled (usd per share)	34.38
Forfeited (usd per share)	34.50
Outstanding at December 31, 2017 (usd per share)	34.34	$ 34.53
Vested and expected to vest at December 31, 2017 (usd per share)	34.34
Convertible at December 31, 2017 (usd per share)	$ 34.59
Aggregate Intrinsic Value
Vested and expected to vest at December 31, 2018	$ 35
Non-forfeitable at December 31, 2018(1)	$ 10

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Convertible units as of the balance sheet date.

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As of the balance sheet date, the weighted-average fair value for convertible units.

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The number of vested and expected to vest shares as of the balance sheet date.

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As of the balance sheet date, the weighted-average fair value for outstanding units that are fully vested or expected to vest.

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ntrinsic value of convertible equity-based compensation awards. Excludes options.

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Intrinsic value of equity-based compensation awards vested and expected to vest. Excludes options.

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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).

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Number of non-option equity instruments exercised by participants.

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Number of shares under non-option equity instrument agreements that were cancelled as a result of occurrence of a terminating event.

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Net number of non-option equity instruments granted to participants.

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