Supplemental Oil and Gas Disclosures (Unaudited) (Summary of Changes in Reserves - United States) (Details) Mcfe in Millions, Mcf in Millions	12 Months Ended
	Dec. 31, 2020 Mcfe bbl Mcf	Dec. 31, 2019 Mcfe bbl Mcf	Dec. 31, 2018 Mcfe Mcf bbl	Dec. 31, 2018 Mcfe bbl Mcf	Dec. 31, 2018 Mcfe Mcf bbl
Proved Developed and Undeveloped Reserve (Energy) [Roll Forward]
Proved reserves, beginning of period, (bcfe) | Mcfe	12,721	11,921			14,775
Revisions of previous estimates due to price | Mcfe	(4,370)	(717)			154
Extensions, discoveries and other additions | Mcfe	741	1,195			1,009
Production | Mcfe	(880)	(778)			(946)
Acquisition of reserves in place | Mcfe	2,354	0			0
Disposition of reserves in place | Mcfe	0	(2)			(3,443)
Proved reserves, end of period, (bcfe) | Mcfe	11,990	12,721			11,921
Proved undeveloped reserves:
Proved undeveloped reverses (energy) | Mcfe	2,437	929	190	190	190
United States
Proved Developed and Undeveloped Reserves [Roll Forward]
Acquisition of reserves in place			0	0
Proved Developed and Undeveloped Reserve (Energy) [Roll Forward]
Proved reserves, beginning of period, (bcfe) | Mcfe	12,721	11,921			14,775
Revisions of previous estimates due to price | Mcfe	(4,370)	(717)			154
Revisions of previous estimates other than price | Mcfe	1,424	1,102			372
Extensions, discoveries and other additions | Mcfe	741	1,195			1,009
Production | Mcfe	(880)	(778)			(946)
Acquisition of reserves in place | Mcfe	2,354	0			0
Disposition of reserves in place | Mcfe	0	(2)			(3,443)
Proved reserves, end of period, (bcfe) | Mcfe	11,990	12,721			11,921
Proved developed reserves as of:
Proved developed reserves (energy) | Mcfe	8,203	6,421	5,557	5,557	5,557
Proved undeveloped reserves:
Proved undeveloped reverses (energy) | Mcfe	3,787	6,300	6,364	6,364	6,364
United States | Natural Gas
Proved Developed and Undeveloped Reserves [Roll Forward]
Proved reserves, beginning of year | Mcf	8,630	8,044	11,126
Revisions of previous estimates due to price | Mcf	(2,143)	(480)	96
Revisions of previous estimates other than price | Mcf	763	685	316
Extensions, discoveries and other additions | Mcf	714	992	753
Production | Mcf	(694)	(609)	(807)
Acquisition of reserves in place | Mcf	1,911	0
Disposition of reserves in place | Mcf	0	(2)	(3,440)
Proved reserves, end of year | Mcf	9,181	8,630	8,044
Proved developed reserves as of:
Proved developed reserves (volume) | Mcf	6,342	4,906	4,395	4,395	4,395
Proved undeveloped reserves:
Proved undeveloped reserves (volume) | Mcf	2,839	3,724	3,649	3,649	3,649
United States | Oil
Proved Developed and Undeveloped Reserves [Roll Forward]
Proved reserves, beginning of year	72,925,000	69,007,000		65,636,000
Revisions of previous estimates due to price	(32,507,000)	(2,041,000)		788,000
Revisions of previous estimates other than price	3,816,000	3,707,000		410,000
Extensions, discoveries and other additions	135,000	6,948,000		5,830,000
Production	(5,141,000)	(4,696,000)		(3,407,000)
Acquisition of reserves in place	18,796,000	0
Disposition of reserves in place	0	0		(250,000)
Proved reserves, end of year	58,024,000	72,925,000		69,007,000
Proved developed reserves as of:
Proved developed reserves (volume)	33,563,000	26,124,000	18,037,000	18,037,000	18,037,000
Proved undeveloped reserves:
Proved undeveloped reserves (volume)	24,461,000	46,801,000	50,970,000	50,970,000	50,970,000
United States | NGL
Proved Developed and Undeveloped Reserves [Roll Forward]
Proved reserves, beginning of year	608,761,000	577,063,000		542,455,000
Revisions of previous estimates due to price	(338,639,000)	(37,492,000)		8,912,000
Revisions of previous estimates other than price	106,444,000	65,869,000		8,855,000
Extensions, discoveries and other additions	4,371,000	26,941,000		36,823,000
Production	(25,927,000)	(23,620,000)		(19,706,000)
Acquisition of reserves in place	55,141,000	0
Disposition of reserves in place	0	0		(276,000)
Proved reserves, end of year	410,151,000	608,761,000		577,063,000
Proved developed reserves as of:
Proved developed reserves (volume)	276,548,000	226,271,000	175,480,000	175,480,000	175,480,000
Proved undeveloped reserves:
Proved undeveloped reserves (volume)	133,603,000	382,490,000	401,583,000	401,583,000	401,583,000