Supplemental Oil and Gas Disclosures (Summary of Changes in Reserves - United States) (Details) Mcfe in Millions, Mcf in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2019 Mcfe Mcf bbl	Dec. 31, 2019 Mcfe Mcf bbl	Dec. 31, 2019 USD ($) Mcfe Mcf bbl	Dec. 31, 2019 Mcfe Mcf bbl	Dec. 31, 2018 USD ($) Mcfe bbl Mcf	Dec. 31, 2017 Mcfe bbl Mcf	Dec. 31, 2017 Mcfe bbl Mcf	Dec. 31, 2017 USD ($) Mcfe bbl Mcf	Dec. 31, 2017 Mcfe bbl Mcf
Proved Developed and Undeveloped Reserves [Roll Forward]
Acquisition of reserve in place		0		0			0		0
Revisions of previous quantity estimates | $			$ 152		$ 361			$ 1,721
Proved Developed and Undeveloped Reserve (Energy) [Roll Forward]
Proved reserves, beginning of period, (bcfe) | Mcfe	11,921				14,775	5,253
Revisions of previous estimates due to price | Mcfe	(717)				154	1,691
Extensions, discoveries and other additions | Mcfe	1,195				1,009	8,087
Production | Mcfe	(778)				(946)	(897)
Acquisition of reserves in place | Mcfe	0				0	0
Disposition of reserves in place | Mcfe	(2)				(3,443)	0
Proved reserves, end of period, (bcfe) | Mcfe	12,721				11,921	14,775
Proved undeveloped reserves:
Proved undeveloped reverses (energy) | Mcfe	929	929	929	929	190	1,375	1,375	1,375	1,375
United States
Proved Developed and Undeveloped Reserve (Energy) [Roll Forward]
Proved reserves, beginning of period, (bcfe) | Mcfe	11,921				14,775	5,253
Revisions of previous estimates due to price | Mcfe	(717)				154	1,691
Revisions of previous estimates other than price | Mcfe	1,102				372	641
Extensions, discoveries and other additions | Mcfe	1,195				1,009	8,087
Production | Mcfe	(778)				(946)	(897)
Acquisition of reserves in place | Mcfe					0
Disposition of reserves in place | Mcfe	(2)				(3,443)	0
Proved reserves, end of period, (bcfe) | Mcfe	12,721				11,921	14,775
Proved developed reserves:
Proved developed reserves (energy) | Mcfe	6,421	6,421	6,421	6,421	5,557	7,920	7,920	7,920	7,920
Proved undeveloped reserves:
Proved undeveloped reverses (energy) | Mcfe	6,300	6,300	6,300	6,300	6,364	6,855	6,855	6,855	6,855
United States | Natural Gas
Proved Developed and Undeveloped Reserves [Roll Forward]
Proved reserves, beginning of year | Mcf		8,044			11,126		4,866
Revisions of previous estimates due to price | Mcf		(480)			96		1,327
Revisions of previous estimates other than price | Mcf		685			316		571
Extensions, discoveries and other additions | Mcf		992			753		5,159
Production | Mcf		(609)			(807)		(797)
Acquisition of reserve in place | Mcf					0
Disposition of reserves in place | Mcf		(2)			(3,440)		0
Proved reserves, end of year | Mcf		8,630			8,044		11,126
Proved developed reserves:
Proved developed reserves (volume) | Mcf	4,906	4,906	4,906	4,906	4,395	6,979	6,979	6,979	6,979
Proved undeveloped reserves:
Proved undeveloped reserves (volume) | Mcf	3,724	3,724	3,724	3,724	3,649	4,147	4,147	4,147	4,147
United States | Oil
Proved Developed and Undeveloped Reserves [Roll Forward]
Proved reserves, beginning of year				69,007,000	65,636,000				10,523,000
Revisions of previous estimates due to price				(2,041,000)	788,000				3,197,000
Revisions of previous estimates other than price				3,707,000	410,000				(1,529,000)
Extensions, discoveries and other additions				6,948,000	5,830,000				55,772,000
Production				(4,696,000)	(3,407,000)				(2,327,000)
Acquisition of reserve in place					0
Disposition of reserves in place				0	(250,000)				0
Proved reserves, end of year				72,925,000	69,007,000				65,636,000
Proved developed reserves:
Proved developed reserves (volume)	26,124,000	26,124,000	26,124,000	26,124,000	18,037,000	14,513,000	14,513,000	14,513,000	14,513,000
Proved undeveloped reserves:
Proved undeveloped reserves (volume)	46,801,000	46,801,000	46,801,000	46,801,000	50,970,000	51,123,000	51,123,000	51,123,000	51,123,000
United States | NGL
Proved Developed and Undeveloped Reserves [Roll Forward]
Proved reserves, beginning of year				577,063,000	542,455,000				53,931,000
Revisions of previous estimates due to price				(37,492,000)	8,912,000				57,447,000
Revisions of previous estimates other than price				65,869,000	8,855,000				13,102,000
Extensions, discoveries and other additions				26,941,000	36,823,000				432,220,000
Production				(23,620,000)	(19,706,000)				(14,245,000)
Acquisition of reserve in place					0
Disposition of reserves in place				0	(276,000)				0
Proved reserves, end of year				608,761,000	577,063,000				542,455,000
Proved developed reserves:
Proved developed reserves (volume)	226,271,000	226,271,000	226,271,000	226,271,000	175,480,000	142,213,000	142,213,000	142,213,000	142,213,000
Proved undeveloped reserves:
Proved undeveloped reserves (volume)	382,490,000	382,490,000	382,490,000	382,490,000	401,583,000	400,242,000	400,242,000	400,242,000	400,242,000