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Master Limited Partnership (Details) - USD ($) $ / shares in Units, $ in Millions		3 Months Ended						9 Months Ended
	Jul. 30, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2019	Sep. 30, 2018
Equity transactions of MPLX & ANDX		$ (596)	$ 1	$ 2	$ 0	$ 0	$ (546)
Preferred Partner | Preferred Class B
Distribution declared, per unit	$ 68.75
Additional Paid-in Capital
Equity transactions of MPLX & ANDX	$ (55)	$ (691)	$ 2	$ 3	$ 1	$ 1	$ 2,380	$ (686)	$ 2,382
Deferred income tax impact from changes in equity	$ (642)							$ (634)	$ (546)
Public
Common units conversion ratio	1.135
Nonpublic
Common units conversion ratio	1.0328
MPLX
MPC's partnership interest in MLP (in percentage)		63.00%						63.00%
MPLX | Series B Preferred Stock
Preferred units, outstanding	600,000
ANDX
Preferred units, outstanding	600,000

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Ratio applied to the conversion of ANDX common units to MPLX common units

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- Definition

Per unit of ownership amount of cash distributions declared to unit-holder of a limited partnership (LP).

+ References

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
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-Paragraph 1
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