XML 15 R55.htm IDEA: XBRL DOCUMENT v2.4.0.6
Variable Interest Entities - Royalty Trusts - Assets and Liabilities Included in Unaudited Condensed Consolidated Balance Sheets (Parenthetical) (Details) (Royalty Trusts, USD $)
In Millions, unless otherwise specified
Mar. 31, 2013
Dec. 31, 2012
Royalty Trusts
   
Variable Interest Entity [Line Items]    
Reserves for expenses $ 3.0 $ 3.0