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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
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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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- Definition ntrinsic value of convertible equity-based compensation awards. Excludes options. + References No definition available. + Details
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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 + Details
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- Definition Number of equity instruments other than options outstanding, including both vested and non-vested instruments. + 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)(ii) -URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901 Reference 2: 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 + Details
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