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Future Minimum Lease Payments for Capital and Operating Leases (Parenthetical) (Detail) (USD $)
In Millions, unless otherwise specified
12 Months Ended
Dec. 31, 2012
Mainline
 
Capital Leases And Operating Leases [Line Items]  
Number of assets subject to lease 49
Regional Carrier
 
Capital Leases And Operating Leases [Line Items]  
Number of assets subject to lease 38
Nonoperating Aircraft
 
Capital Leases And Operating Leases [Line Items]  
Number of assets subject to lease 25
Operating lease future payments 130
Minimum
 
Capital Leases And Operating Leases [Line Items]  
Imputed interest rate 3.30%
Maximum
 
Capital Leases And Operating Leases [Line Items]  
Imputed interest rate 20.00%