Property, Plant and Equipment - Narrative (Details)	1 Months Ended		3 Months Ended	7 Months Ended	12 Months Ended						13 Months Ended
	Jun. 30, 2019 USD ($)	Dec. 31, 2018 USD ($) MMBoe	Dec. 31, 2019 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($) MMBoe		Dec. 31, 2017 USD ($)		Dec. 31, 2016 USD ($)	Dec. 31, 2019 USD ($)	Jul. 31, 2019 USD ($)	May 31, 2019 MMBoe
Property, Plant and Equipment [Line Items]
Proceeds from sales of property, plant and equipment					$ 20,382,000	$ 1,175,000	[1]	$ 69,506,000	[1]
Asset retirement obligation settled					25,544,000	11,510,000
Gain (loss) on sale of assets					227,000	54,000	[1]	127,434,000	[1]
Cost of acquired assets					1,280,100,000	797,300,000		71,100,000
Impairment of assets					0	20,000,000	[1],[2]	0	[1],[2]
Total capitalized exploratory well costs		$ 207,855,000	$ 217,326,000	$ 217,326,000	217,326,000	$ 207,855,000		155,103,000		$ 101,546,000	$ 217,326,000
Exploratory well costs capitalized more than one year			153,900,000	153,900,000	153,900,000						153,900,000
MP Gulf of Mexico LLC
Property, Plant and Equipment [Line Items]
Parent ownership interest		80.00%				80.00%
MP Gulf of Mexico LLC | PAI (Final)
Property, Plant and Equipment [Line Items]
Noncontrolling ownership interest		20.00%				20.00%
LLOG Exploration Offshore L.L.C. and LLOG Bluewater Holdings, L.L.C. [Member]
Property, Plant and Equipment [Line Items]
Proved reserves | MMBoe													67
Acquisition, cash paid	$ 1,238,400,000			1,238,353,000
LLOG Exploration Offshore L.L.C. and LLOG Bluewater Holdings, L.L.C. [Member] | Sales Thresholds 2019 to 2025
Property, Plant and Equipment [Line Items]
Contingent consideration, maximum			200,000,000	200,000,000	200,000,000						200,000,000
LLOG Exploration Offshore L.L.C. and LLOG Bluewater Holdings, L.L.C. [Member] | Net crude oil and condensate revenue
Property, Plant and Equipment [Line Items]
Contingent consideration, maximum			50,000,000	50,000,000	50,000,000						50,000,000
PAI (Final)
Property, Plant and Equipment [Line Items]
Proved reserves | MMBoe		97				97
Acquisition, cash paid		$ 780,700,000									780,678,000
PAI (Final) | Sales Thresholds 2019 to 2025
Property, Plant and Equipment [Line Items]
Contingent consideration, maximum		150,000,000	150,000,000	150,000,000	150,000,000	$ 150,000,000					150,000,000
PAI (Final) | Enhanced Oil Recovery Projects
Property, Plant and Equipment [Line Items]
Contingent consideration, maximum		$ 50,000,000				50,000,000
Athabasca Oil Corporation
Property, Plant and Equipment [Line Items]
Cost of acquired assets, cash paid										206,700,000
Athabasca Oil Corporation | Canadian Subsidiary
Property, Plant and Equipment [Line Items]
Cost of acquired assets										375,000,000.0
Western Canada
Property, Plant and Equipment [Line Items]
Proceeds from sales of property, plant and equipment								48,800,000
Asset retirement obligation settled								85,900,000
Gain (loss) on sale of assets								129,000,000.0
Kaybob Duvernay Lands, Alberta | Athabasca Oil Corporation
Property, Plant and Equipment [Line Items]
Cost of acquired assets, carried interest										$ 168,000,000.0
Carried interest paid			152,700,000	152,700,000	152,700,000						152,700,000
Kaybob Duvernay Lands, Alberta | Athabasca Oil Corporation | Canadian Subsidiary
Property, Plant and Equipment [Line Items]
Interest in assets acquired										70.00%
United States - Onshore
Property, Plant and Equipment [Line Items]
Impairment of assets					0	20,000,000		0
Placid Montney Lands, Alberta | Athabasca Oil Corporation | Canadian Subsidiary
Property, Plant and Equipment [Line Items]
Interest in assets acquired										30.00%
Brunei
Property, Plant and Equipment [Line Items]
Exploratory well costs capitalized more than one year			57,500,000	57,500,000	57,500,000						57,500,000
Vietnam
Property, Plant and Equipment [Line Items]
Exploratory well costs capitalized more than one year			69,100,000	69,100,000	69,100,000						69,100,000
United States
Property, Plant and Equipment [Line Items]
Cost of acquired assets					1,266,900,000	797,100,000		58,100,000
Exploratory well costs capitalized more than one year			27,400,000	$ 27,400,000	27,400,000						$ 27,400,000
Malaysia
Property, Plant and Equipment [Line Items]
Disposal group including discontinued operation, consideration												$ 2,000,000,000.0
Gain (loss) on disposition of business			$ 985,400,000		985,400,000
Disposal group including discontinued operation, contingent consideration paid												$ 100,000,000.0
Cost of acquired assets					$ 0	$ 0		$ 0

[1] Reclassified to conform with current presentation (see Note E)

[2] ¹ Reclassified to conform with current presentation (see Notes C and E). 2017 revenue is presented net of $58.9 million of transportation, gathering and processing costs as historically shown prior to the adoption of ASC 606 on January 1, 2018. See Notes to Consolidated Financial Statements, page 58.