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Consolidated Statements of Comprehensive Income (Parenthetical) (USD $)
In Millions, unless otherwise specified
3 Months Ended 9 Months Ended
Sep. 30, 2012
Sep. 30, 2011
Sep. 30, 2012
Sep. 30, 2011
Statement of Other Comprehensive Income [Abstract]        
Net loss arising during period, tax benefit       $ 3   
Amortization of net loss included in net income, tax expense (benefit) $ 1 $ 1 $ 4 $ 2