Schedule II - Valuation and Qualifying Accounts (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Allowance for doubtful accounts
Valuation and qualifying accounts
Balance at Beginning of Period	$ 788	$ 668	$ 594
Charged to Costs and Expenses	37	126	77
Charged to Other Accounts	(3)	(6)	(3)
Deductions	0	0	0
Balance at End of Period	822	788	668
Valuation allowance and reserves, current	42	22	24
Environmental, litigation and other reserves
Valuation and qualifying accounts
Balance at Beginning of Period	2,411	994	935
Charged to Costs and Expenses	115	182	140
Charged to Other Accounts	43	1,408	85
Deductions	(140)	(173)	(166)
Balance at End of Period	2,429	2,411	994
Environmental litigation tax and other reserves, current	$ 149	$ 188	$ 146