Derivative and Hedging Activities - Marketing Revenues (Details) - USD ($) $ in Millions	3 Months Ended			6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018		Jun. 30, 2019	Jun. 30, 2018
Derivative [Line Items]
Revenues	$ 1,179	$ 1,233		$ 2,409	$ 2,593
Losses on undesignated marketing natural gas derivatives	275	(251)		(26)	(368)
Revenues	2,386	2,289	[1]	4,582	4,813	[1]
Marketing, Gathering And Compression | Other contract
Derivative [Line Items]
Losses on undesignated marketing natural gas derivatives	(1)	0		(3)	0
Marketing | Marketing, Gathering And Compression
Derivative [Line Items]
Revenues	917	1,273		2,152	2,519
Marketing
Derivative [Line Items]
Revenues	824	1,069		1,967	2,158
Losses on undesignated marketing natural gas derivatives	(1)			(3)
Revenues	$ 916	$ 1,273	[1]	$ 2,149	$ 2,519	[1]

[1] Financial information for 2018 has been recast to reflect the retrospective application of the successful efforts method of accounting. See Note 1.