Fair Value Measurements (Narrative) (Details) (Categories of Investments, Marketable Securities, Trading Securities [Member], USD $) In Millions, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
PLUM CREEK TIMBER CO INC [Member]
Deferred Compensation Obligations Included in Other Liabilities	$ 5	$ 5
PLUM CREEK TIMBERLANDS L P [Member]
Deferred Compensation Obligations Included in Other Liabilities	$ 5	$ 5