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Reconciliation of Unrecognized Tax Benefits (Detail) (USD $)
In Millions, unless otherwise specified
12 Months Ended
Dec. 31, 2012
Dec. 31, 2011
Dec. 31, 2010
Income Tax Contingency [Line Items]      
Balance at January 1, $ 24 $ 32 $ 16
Decrease in unrecognized tax benefits relating to settlements with taxing authorities (12)    
Increase (decrease) in unrecognized tax benefits as a result of tax positions taken during a prior period 8 (9)  
Decrease in unrecognized tax benefits relating from a lapse of the statute of limitations (1)    
Increase due to Continental's uncertain tax positions at the Merger closing date     6
Increase in unrecognized tax benefits as a result of tax positions taken during the current period   1 10
Balance at December 31, $ 19 $ 24 $ 32