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Consolidated Statements of Comprehensive Income (Unaudited) (Parenthetical) (USD $)
In Millions, unless otherwise specified
3 Months Ended
Mar. 31, 2013
Mar. 31, 2012
Change in amortization of accumulated actuarial losses, net of tax expense $ 2 $ 2
Change in fuel hedge mark-to-market, net of tax expense/(benefit) $ 0 $ (4)