Income Taxes (Schedule of Deferred Tax Assets and Liabilities) (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Postretirement benefit accruals	$ 102	$ 165
Pension obligations	516	1,344
Alternative minimum and other tax credits	416	270
Net operating and capital loss carryforwards	665	662
Compensation reserves	174	257
Other	139	251
Gross deferred income tax assets	2,012	2,949
Less: valuation allowance (a)	(429)	(403)
Net deferred income tax asset	1,583	2,546
Intangibles	(139)	(231)
Plants, properties and equipment	(2,000)	(2,828)
Forestlands, related installment sales, and investment in subsidiary	(1,454)	(2,260)
Gross deferred income tax liabilities	(3,593)	(5,319)
Net deferred income tax liability	$ (2,010)	$ (2,773)