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Equity-Based Compensation (Tables)

12 Months Ended

Dec. 31, 2018

Phantom Units

Equity-Based Compensation [Line Items]

Summary of Unit Award Activity

The following is a summary of phantom unit award activity of MPLX LP common units in 2018:

		Phantom Units
		Number of Units			Weighted Average Fair Value				Aggregate Intrinsic Value (In millions)
Outstanding at December 31, 2017		1,351,523			$	34.53
Granted		437,092			33.84
Settled		(509,570	)		34.38
Forfeited		(124,710	)		34.50
Outstanding at December 31, 2018		1,154,335			34.34
Vested and expected to vest at December 31, 2018		1,139,877			34.34				$	35
Non-forfeitable at December 31, 2018(1)		321,638			$	34.59			$	10

Schedule of Share-based Compensation Arrangement by Share-based Payment Award, Restricted Stock Units, Vested and Expected to Vest

The following is a summary of the values related to phantom units:

		Phantom Units
		Intrinsic Value of Units Issued During the Period (in millions)				Weighted Average Grant Date Fair Value of Units Granted During the Period
2018		$	18			$	33.84
2017		15				36.26
2016		$	5			$	29.42

Performance Shares

Equity-Based Compensation [Line Items]

Summary of Unit Award Activity

The following table presents a summary of the 2018 activity for performance unit awards to be settled in MPLX LP common units:

		Performance Units
		Number of Units			Weighted Average Fair Value
Outstanding at December 31, 2017		2,536,594			$	0.85
Granted		—			—
Settled		(538,594	)		1.04
Forfeited		(56,250	)		0.90
Outstanding at December 31, 2018		1,941,750			0.80

Schedule of Share-based Compensation, Performance Unit Awards, Valuation Assumptions

The following table provides a summary of the weighted average inputs used for these assumptions:

		2018		2017		2016
Risk-free interest rate		N/A		1.52%		0.96%
Look-back period		N/A		2.83 years		2.83 years
Expected volatility		N/A		49.34%		47.59%
Grant date fair value of performance units granted		N/A		$0.90		$0.63

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