Master Limited Partnerships (MPLX-Private Placement of Preferred Units) (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions		12 Months Ended
	May 13, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Noncontrolling Interest [Line Items]
Issuance of MPLX LP redeemable preferred units		$ 0	$ 0	$ 984
Series A Convertible Preferred Units | MPLX
Noncontrolling Interest [Line Items]
Preferred units, dividend rate, percentage	6.50%
Issuance of MPLX LP redeemable preferred units	$ 984
Preferred units, dividend rate, per-dollar-amount	$ 0.528125
Series A Convertible Preferred Units | MPLX | Preferred Units
Noncontrolling Interest [Line Items]
Sale of units (number of units)	30.8
Units issued, price per unit	$ 32.50