Sales to Related Parties (Detail) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Related Party Transaction [Line Items]
Rental income - related parties		$ 241	$ 293	$ 712	$ 904
Other income - related parties		63	31	190	84
MPC
Related Party Transaction [Line Items]
Rental income - related parties		241	293	712	904
Other income - related parties		48	14	144	34
Product sales to MPC that net to zero		107	301	332	819
Other Affiliates [Member]
Related Party Transaction [Line Items]
Other income - related parties		15	17	46	50
Product [Member]
Related Party Transaction [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax, Related Parties		37	32	100	109
Product [Member] | MPC
Related Party Transaction [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax, Related Parties	[1]	37	32	100	109
Service [Member]
Related Party Transaction [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax, Related Parties		909	899	2,694	2,549
Service [Member] | MPC
Related Party Transaction [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax, Related Parties		908	899	2,692	2,549
Service [Member] | Other Affiliates [Member]
Related Party Transaction [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax, Related Parties		$ 1	$ 0	$ 2	$ 0

[1] There were additional product sales to MPC that net to zero within the consolidated financial statements as the transactions are recorded net due to the terms of the agreements under which such product was sold. For the three and nine months ended September 30, 2020, these sales totaled $107 million and $332 million, respectively. For the three and nine months ended September 30, 2019, these sales totaled $301 million and $819 million, respectively.