Supplemental Cash Flow Information (Details) - USD ($) $ in Millions	1 Months Ended	12 Months Ended
	Jan. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Decrease (increase) in current assets:
Receivables, net		$ 1,294	$ 2,753	$ (753)
Inventories		(222)	(1,014)	(13)
Income taxes receivable		(104)	(23)	10
Prepaid expenses and other		(45)	(32)	2
Increase (decrease) in current liabilities:
Accounts payable		(1,787)	(3,149)	977
Accrued expenses		(40)	38	53
Taxes other than income taxes		(74)	(64)	337
Income taxes payable		(328)	(319)	309
Changes in current assets and current liabilities		(1,306)	(1,810)	922
Cash Flows Related to Interest and Income Taxes
Interest paid in excess of amount capitalized		416	392	361
Income taxes paid, net		2,093	$ 1,624	$ 387
Supplemental Cash Flow Elements [Textual]
Treasury stock purchased but settled in subsequent quarter		$ 25
Subsequent Event [Member]
Supplemental Cash Flow Elements [Textual]
Stock purchases, in shares	347,438