Pending Merger With Deltic (Narrative) (Details) shares in Millions, $ in Millions		12 Months Ended
	Oct. 22, 2017 USD ($) a shares	Dec. 31, 2017
Business Acquisition [Line Items]
Date of merger agreement		Oct. 22, 2017
Deltic [Member]
Business Acquisition [Line Items]
Business acquisition, share price	180.00%
Acres of timberland | a	530,000
Estimated total consideration expected to be issued | shares	22
Merger termination fee, obligation payable	$ 66
Merger termination fee, obligation receivable	$ 33
Earnings and profits dividend rate or special distribution percentage of stock	80.00%
Earnings and profits dividend rate or special distribution percentage of cash	20.00%