Schedule II - Valuation and Qualifying Accounts (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Allowance for excess and obsolete materials and supplies
Reserves and allowances deducted from asset accounts
Balance at the beginning of the period	$ 134	$ 141	$ 153
Charge to cost and expenses	3	12	24
Deductions	10	19	36
Balance at the end of the period	127	134	141
Valuation allowance on deferred tax assets
Reserves and allowances deducted from asset accounts
Balance at the beginning of the period	681	574	412
Charge to cost and expenses	37	67	162
Charge to other accounts		40
Deductions	2
Balance at the end of the period	$ 716	681	$ 574
Valuation allowance adjustment		26
Valuation allowance in business combination		$ 14