Impairments (Income Statement Location of Impairments) (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2020	Dec. 31, 2020		Dec. 31, 2019
Finite-Lived Intangible Assets [Line Items]
Goodwill, impairment loss	$ 7,330	$ 7,394	[1]	$ 1,197	[1]
Equity method investment, other than temporary impairment	$ 1,315
Impairment charges		9,741		1,239
Impairment expense
Finite-Lived Intangible Assets [Line Items]
Goodwill, impairment loss		7,394		1,197
Impairment of long-lived assets held-for-use		1,032	[2]	0
Income (loss) from equity method investments
Finite-Lived Intangible Assets [Line Items]
Equity method investment, other than temporary impairment		$ 1,315		$ 42

[1] See Note 7.

[2] The remaining difference not described in the narrative below is related to certain immaterial Midstream assets.