Supplemental Oil and Gas Information (Unaudited) - Summary of Proved Reserves Based on Average Prices (Details) MMBbls in Millions, ft³ in Billions	12 Months Ended
	Dec. 31, 2020 MMBbls ft³	Dec. 31, 2019 MMBbls ft³	Dec. 31, 2018 ft³ MMBbls	Dec. 31, 2017 MMBbls ft³
Proved developed and undeveloped oil reserves:
Proved developed reserves	410.8	472.3	430.2	346.7
Proved undeveloped reserves	304.1	352.7	413.8	351.5
Crude Oil
Proved developed and undeveloped oil reserves:
Proved developed and undeveloped crude oil/synthetic oil reserves, beginning balance	825.0	844.0	698.2
Revisions of previous estimates	(194.7)	28.4	(21.8)
Improved recovery			0.9
Extensions and discoveries	150.3	73.3	122.6
Purchases of properties		76.2	106.9
Sales of properties	(1.7)	(121.5)
Production	(63.9)	(75.4)	(62.8)
Proved developed and undeveloped reserves, ending balance	714.9	825.0	844.0
Net crude oil and condensate revenue | Crude Oil
Proved developed and undeveloped oil reserves:
Proved developed and undeveloped crude oil/synthetic oil reserves, beginning balance	423.9	432.5	328.1
Revisions of previous estimates	(137.4)	(31.0)	(15.3)
Improved recovery			0.8
Extensions and discoveries	19.6	58.2	58.9
Purchases of properties		56.3	93.6
Sales of properties	(1.5)
Production	(38.1)	(46.3)	(33.6)
Proved developed and undeveloped reserves, ending balance	266.5	423.9	432.5
Proved developed reserves	179.8	230.9	249.3	185.5
Proved undeveloped reserves	86.7	193.0	183.2	142.6
Net natural gas liquids revenue
Proved developed and undeveloped oil reserves:
Proved developed and undeveloped crude oil/synthetic oil reserves, beginning balance	56.1	54.2	48.9
Revisions of previous estimates	(16.4)	(5.0)	(6.2)
Extensions and discoveries	2.8	6.8	12.0
Purchases of properties		5.2	3.0
Sales of properties	(0.1)
Production	(4.2)	(4.5)	(3.5)
Proved developed and undeveloped reserves, ending balance	38.2	56.1	54.2
Proved developed reserves	28.7	28.1	27.3	24.6
Proved undeveloped reserves	9.5	28.0	26.9	24.3
Net natural gas revenue
Proved developed and undeveloped oil reserves:
Proved developed and undeveloped crude oil/synthetic oil reserves, beginning balance | ft³	2,069.7	2,143.6	1,927.1
Revisions of previous estimates | ft³	(245.4)	386.5	(1.8)
Extensions and discoveries | ft³	767.2	49.8	310.3
Purchases of properties | ft³		88.3	61.7
Sales of properties | ft³	(0.7)
Production | ft³	(129.8)	(147.8)	(154.3)
Proved developed and undeveloped reserves, ending balance | ft³	2,461.0	2,069.7	2,143.6
Proved developed reserves | ft³	1,213.8	1,279.8	921.6	819.3
Proved undeveloped reserves | ft³	1,247.2	789.9	1,222.0	1,107.8
MP Gulf of Mexico LLC
Proved developed and undeveloped oil reserves:
Proved developed and undeveloped reserves, ending balance	17.4
Proved developed reserves	14.2
Proved undeveloped reserves	3.2
MP Gulf of Mexico LLC | Net crude oil and condensate revenue
Proved developed and undeveloped oil reserves:
Proved developed and undeveloped reserves, ending balance	15.6
Proved developed reserves	12.7
Proved undeveloped reserves	2.9
MP Gulf of Mexico LLC | Net natural gas liquids revenue
Proved developed and undeveloped oil reserves:
Proved developed and undeveloped reserves, ending balance	0.7
Proved developed reserves	0.6
Proved undeveloped reserves	0.1
MP Gulf of Mexico LLC | Net natural gas revenue
Proved developed and undeveloped oil reserves:
Proved developed and undeveloped reserves, ending balance | ft³	6.5
Proved developed reserves | ft³	5.7
Proved undeveloped reserves | ft³	0.8
Noncontrolling interest volume | ft³	1.6
U.S.
Proved developed and undeveloped oil reserves:
Proved developed reserves	230.3	273.4	247.0	170.9
Proved undeveloped reserves	98.2	226.7	178.7	134.0
U.S. | Crude Oil
Proved developed and undeveloped oil reserves:
Proved developed and undeveloped crude oil/synthetic oil reserves, beginning balance	500.1	425.6	304.9
Revisions of previous estimates	(146.6)	(17.9)	(14.0)
Improved recovery			0.0
Extensions and discoveries	19.5	62.2	60.1
Purchases of properties		76.2	98.7
Sales of properties	(1.7)	(0.1)
Production	(42.8)	(45.9)	(24.0)
Proved developed and undeveloped reserves, ending balance	328.5	500.1	425.6
U.S. | Net crude oil and condensate revenue | Crude Oil
Proved developed and undeveloped oil reserves:
Proved developed and undeveloped crude oil/synthetic oil reserves, beginning balance	377.8	326.5	224.7
Revisions of previous estimates	(116.8)	(17.1)	(15.0)
Improved recovery			0.0
Extensions and discoveries	14.5	49.2	42.9
Purchases of properties		56.3	92.3
Sales of properties	(1.5)
Production	(33.4)	(37.0)	(18.4)
Proved developed and undeveloped reserves, ending balance	240.6	377.8	326.5
Proved developed reserves	161.4	205.0	189.0	126.3
Proved undeveloped reserves	79.2	172.8	137.5	98.4
U.S. | Net natural gas liquids revenue
Proved developed and undeveloped oil reserves:
Proved developed and undeveloped crude oil/synthetic oil reserves, beginning balance	52.8	47.6	43.0
Revisions of previous estimates	(17.1)	(2.5)	(5.3)
Extensions and discoveries	2.7	6.4	9.7
Purchases of properties		5.2	3.0
Sales of properties	(0.1)
Production	(3.7)	(3.9)	(2.8)
Proved developed and undeveloped reserves, ending balance	34.6	52.8	47.6
Proved developed reserves	25.5	26.2	24.9	23.3
Proved undeveloped reserves	9.1	26.6	22.7	19.7
U.S. | Net natural gas revenue
Proved developed and undeveloped oil reserves:
Proved developed and undeveloped crude oil/synthetic oil reserves, beginning balance | ft³	416.8	309.0	223.3
Revisions of previous estimates | ft³	(76.2)	10.3	37.6
Extensions and discoveries | ft³	14.0	39.5	44.7
Purchases of properties | ft³		88.3	20.3
Sales of properties | ft³	(0.7)
Production | ft³	(34.4)	(30.2)	(16.9)
Proved developed and undeveloped reserves, ending balance | ft³	319.5	416.8	309.0
Proved developed reserves | ft³	260.2	253.1	198.3	127.7
Proved undeveloped reserves | ft³	59.3	163.7	110.7	95.6
Noncontrolling interest volume | ft³	72.0
Canada
Proved developed and undeveloped oil reserves:
Proved developed reserves	180.5	198.1	124.2	114.1
Proved undeveloped reserves	205.9	126.0	164.5	145.1
Canada | Crude Oil
Proved developed and undeveloped oil reserves:
Proved developed and undeveloped crude oil/synthetic oil reserves, beginning balance	324.1	288.6	259.2
Revisions of previous estimates	(47.3)	46.1	(18.1)
Improved recovery			0.0
Extensions and discoveries	130.7	11.1	61.8
Purchases of properties		0.0	6.9
Sales of properties	0.0	0.0
Production	(21.1)	(21.7)	(21.1)
Proved developed and undeveloped reserves, ending balance	386.4	324.1	288.6
Canada | Net crude oil and condensate revenue | Crude Oil
Proved developed and undeveloped oil reserves:
Proved developed and undeveloped crude oil/synthetic oil reserves, beginning balance	45.3	55.0	51.5
Revisions of previous estimates	(19.8)	(14.0)	(8.0)
Improved recovery			0.0
Extensions and discoveries	5.1	9.0	16.0
Purchases of properties		0.0	0.0
Sales of properties	0.0
Production	(4.7)	(4.7)	(4.5)
Proved developed and undeveloped reserves, ending balance	25.9	45.3	55.0
Proved developed reserves	18.4	25.1	23.3	21.9
Proved undeveloped reserves	7.5	20.2	31.7	29.6
Canada | Net natural gas liquids revenue
Proved developed and undeveloped oil reserves:
Proved developed and undeveloped crude oil/synthetic oil reserves, beginning balance	3.3	5.9	5.6
Revisions of previous estimates	0.7	(2.5)	(1.6)
Extensions and discoveries	0.1	0.4	2.3
Purchases of properties		0.0	0.0
Sales of properties	0.0
Production	(0.5)	(0.5)	(0.4)
Proved developed and undeveloped reserves, ending balance	3.6	3.3	5.9
Proved developed reserves	3.2	1.9	1.7	1.0
Proved undeveloped reserves	0.4	1.4	4.2	4.6
Canada | Net natural gas revenue
Proved developed and undeveloped oil reserves:
Proved developed and undeveloped crude oil/synthetic oil reserves, beginning balance | ft³	1,652.9	1,366.4	1,212.4
Revisions of previous estimates | ft³	(169.2)	375.3	(51.2)
Extensions and discoveries | ft³	753.2	10.3	261.0
Purchases of properties | ft³		0.0	41.4
Sales of properties | ft³	0.0
Production | ft³	(95.4)	(99.1)	(97.2)
Proved developed and undeveloped reserves, ending balance | ft³	2,141.5	1,652.9	1,366.4
Proved developed reserves | ft³	953.6	1,026.7	595.0	547.0
Proved undeveloped reserves | ft³	1,187.9	626.2	771.4	665.5
Noncontrolling interest volume | ft³	108.8
Malaysia and Other
Proved developed and undeveloped oil reserves:
Proved developed reserves	0.0	0.8	59.1	61.7
Proved undeveloped reserves	0.0	0.0	70.7	72.4
Malaysia and Other | Crude Oil
Proved developed and undeveloped oil reserves:
Proved developed and undeveloped crude oil/synthetic oil reserves, beginning balance	0.8	129.7	134.1
Revisions of previous estimates	(0.8)	0.3	10.4
Improved recovery			0.9
Extensions and discoveries	0.0	0.0	0.8
Purchases of properties		0.0	1.3
Sales of properties	0.0	(121.4)
Production	0.0	(7.8)	(17.7)
Proved developed and undeveloped reserves, ending balance	0.0	0.8	129.7
Malaysia and Other | Net crude oil and condensate revenue | Crude Oil
Proved developed and undeveloped oil reserves:
Proved developed and undeveloped crude oil/synthetic oil reserves, beginning balance	0.8	51.0	51.9
Revisions of previous estimates	(0.8)	0.1	7.7
Improved recovery			0.8
Extensions and discoveries	0.0	0.0	0.0
Purchases of properties		0.0	1.3
Sales of properties	0.0
Production	0.0	(4.6)	(10.7)
Proved developed and undeveloped reserves, ending balance	0.0	0.8	51.0
Proved developed reserves	0.0	0.8	37.0	37.3
Proved undeveloped reserves	0.0	0.0	14.0	14.6
Malaysia and Other | Net natural gas liquids revenue
Proved developed and undeveloped oil reserves:
Proved developed and undeveloped crude oil/synthetic oil reserves, beginning balance	0.0	0.7	0.3
Revisions of previous estimates	0.0	0.0	0.7
Extensions and discoveries	0.0	0.0	0.0
Purchases of properties		0.0	0.0
Sales of properties	0.0
Production	0.0	(0.1)	(0.3)
Proved developed and undeveloped reserves, ending balance	0.0	0.0	0.7
Proved developed reserves	0.0	0.0	0.7	0.3
Proved undeveloped reserves	0.0	0.0	0.0	0.0
Malaysia and Other | Net natural gas revenue
Proved developed and undeveloped oil reserves:
Proved developed and undeveloped crude oil/synthetic oil reserves, beginning balance | ft³	0.0	468.2	491.4
Revisions of previous estimates | ft³	0.0	0.9	11.8
Extensions and discoveries | ft³	0.0	0.0	4.6
Purchases of properties | ft³		0.0	0.0
Sales of properties | ft³	0.0
Production | ft³	0.0	(18.5)	(40.2)
Proved developed and undeveloped reserves, ending balance | ft³	0.0	0.0	468.2
Proved developed reserves | ft³	0.0	0.0	128.3	144.6
Proved undeveloped reserves | ft³	0.0	0.0	339.9	346.7