Related Party Agreements and Transactions (Summary of Revenue by Income Statement RP Line Item) (Detail) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Related Party Transaction [Line Items]
Rental income - related parties		$ 1,196	$ 846	$ 279
Related Party Transaction, Other Revenues from Transactions with Related Party		114	99	92
MPC
Related Party Transaction [Line Items]
Rental income - related parties		1,196	846	279
Sales Revenue, Goods, Related Party, Net Zero		1,120	607	254
Related Party Transaction, Other Revenues from Transactions with Related Party		47	41	40
Other Affiliates [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Other Revenues from Transactions with Related Party		67	58	52
Service [Member]
Related Party Transaction [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax, Related Parties		3,455	2,404	1,082
Service [Member] | MPC
Related Party Transaction [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax, Related Parties		3,455	2,404	1,082
Product [Member]
Related Party Transaction [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax, Related Parties	[1]	142	87	8
Product [Member] | MPC
Related Party Transaction [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax, Related Parties	[1]	140	87	8
Product [Member] | Other Affiliates [Member]
Related Party Transaction [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax, Related Parties	[1]	$ 2	$ 0	$ 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 2019, 2018 and 2017, these sales totaled $1,120 million, $607 million and $254 million, respectively.