Special Charges - Components of Special Charges (Details) - USD ($) $ in Millions	3 Months Ended			6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017		Jun. 30, 2018	Jun. 30, 2017
Other Income and Expenses [Abstract]
Impairment of assets	$ 111	$ 0		$ 134	$ 0
Severance and benefit costs	11	41		25	78
(Gains) losses on sale of assets and other special charges	7	3		10	17
Special charges	129	44	[1]	169	95	[1]
Income tax benefit related to special charges	(29)	(16)		(38)	(34)
Total special charges, net of tax	$ 100	$ 28		$ 131	$ 61

[1] Amounts adjusted due to the adoption of Accounting Standards Update No. 2014-09, Revenue from Contracts with Customers (Topic 606) and Accounting Standards Update No. 2017-07, Improving the Presentation of Net Periodic Pension Cost and Net Periodic Postretirement Benefit Cost. See Note 1 to the financial statements contained in Part I, Item 1 of this report for additional information.