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Consolidated Statement of Comprehensive Income (Parenthetical) (USD $) In Millions, unless otherwise specified | 12 Months Ended
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Dec. 31, 2014 | Dec. 31, 2013 | Dec. 31, 2012
Deferred taxes on unrealized gain (loss), other, tax effect | $ 0 us-gaap_OtherComprehensiveIncomeLossTaxPortionAttributableToParent1 | $ 7 us-gaap_OtherComprehensiveIncomeLossTaxPortionAttributableToParent1 | $ 3 us-gaap_OtherComprehensiveIncomeLossTaxPortionAttributableToParent1
Deferred taxes on postretirement | 8 us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansTax | 15 us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansTax | (11)us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansTax
Fuel derivatives |  |  |
Deferred taxes on unrealized gain (loss) on derivatives, tax effect | (430)us-gaap_OtherComprehensiveIncomeLossDerivativesQualifyingAsHedgesTax / us-gaap_DerivativeInstrumentRiskAxis = us-gaap_CommodityContractMember | 31 us-gaap_OtherComprehensiveIncomeLossDerivativesQualifyingAsHedgesTax / us-gaap_DerivativeInstrumentRiskAxis = us-gaap_CommodityContractMember | 74 us-gaap_OtherComprehensiveIncomeLossDerivativesQualifyingAsHedgesTax / us-gaap_DerivativeInstrumentRiskAxis = us-gaap_CommodityContractMember
Interest rate derivatives |  |  |
Deferred taxes on unrealized gain (loss) on derivatives, tax effect | $ 5 us-gaap_OtherComprehensiveIncomeLossDerivativesQualifyingAsHedgesTax / us-gaap_DerivativeInstrumentRiskAxis = us-gaap_InterestRateSwapMember | $ 19 us-gaap_OtherComprehensiveIncomeLossDerivativesQualifyingAsHedgesTax / us-gaap_DerivativeInstrumentRiskAxis = us-gaap_InterestRateSwapMember | $ 0 us-gaap_OtherComprehensiveIncomeLossDerivativesQualifyingAsHedgesTax / us-gaap_DerivativeInstrumentRiskAxis = us-gaap_InterestRateSwapMember

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- Definition Amount of tax expense (benefit), after reclassification adjustments, of increase (decrease) in accumulated gain (loss) from derivative instruments designated and qualifying as the effective portion of cash flow hedges and an entity's share of an equity investee's increase (decrease) in deferred hedging gain (loss). + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 10A -Subparagraph (d) -URI http://asc.fasb.org/extlink&oid=36458714&loc=SL7669646-108580 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 12 -URI http://asc.fasb.org/extlink&oid=36458714&loc=d3e640-108580 + Details
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- Definition Amount of tax (expense) benefit, after reclassification adjustments, of (increase) decrease in accumulated other comprehensive (income) loss related to pension and other postretirement defined benefit plans. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 12 -URI http://asc.fasb.org/extlink&oid=36458714&loc=d3e640-108580 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 10A -Subparagraph (i-k) -URI http://asc.fasb.org/extlink&oid=36458714&loc=SL7669646-108580 + Details
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- Definition Amount of tax expense (benefit) allocated to other comprehensive income (loss) attributable to parent entity. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 810 -SubTopic 10 -Section 45 -Paragraph 20 -URI http://asc.fasb.org/extlink&oid=7656940&loc=SL4569643-111683 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 810 -SubTopic 10 -Section 45 -Paragraph 19 -URI http://asc.fasb.org/extlink&oid=7656940&loc=SL4569616-111683 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 810 -SubTopic 10 -Section 50 -Paragraph 1A -Subparagraph (c)(3) -URI http://asc.fasb.org/extlink&oid=18733093&loc=SL4573702-111684 + Details
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