Employee Pension Plans (Component of Pension Cost Recognized in Net Income) (Details) (USD $) In Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010
PLUM CREEK TIMBER CO INC [Member]
Service Cost	$ 2	$ 2	$ 4	$ 4
Interest Cost	2	2	4	4
Expected Return on Plan Assets	(2)	(2)	(4)	(4)
Total Pension Cost	2	2	4	4
PLUM CREEK TIMBERLANDS L P [Member]
Service Cost	2	2	4	4
Interest Cost	2	2	4	4
Expected Return on Plan Assets	(2)	(2)	(4)	(4)
Total Pension Cost	$ 2	$ 2	$ 4	$ 4