Schedule II - Valuation and Qualifying Accounts (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Allowance for doubtful accounts receivable
Reserves and allowances deducted from asset accounts
Balance at the beginning of the period		$ 14	$ 14
Charge to cost and expenses	$ 0	0	0
Deductions		14
Balance at the end of the period			14
Allowance for obsolete materials and supplies
Reserves and allowances deducted from asset accounts
Balance at the beginning of the period	148	109	80
Charge to cost and expenses	15	62	29
Deductions	10	23
Balance at the end of the period	153	148	109
Valuation allowance on deferred tax assets
Reserves and allowances deducted from asset accounts
Balance at the beginning of the period	380	409	329
Charge to cost and expenses	32	10	93
Charge to other accounts		(39)	(13)
Balance at the end of the period	$ 412	$ 380	$ 409