Commitments and Contingencies Commitments and Contingencies - Purchase Obligations (Details) (Fuel contract extension [Member], USD $) In Millions, unless otherwise specified	Aug. 31, 2013
Fuel contract extension [Member]
ContractualObligationFiscalYearMaturityScheduleTable [Line Items]
Purchase obligation, due in fourth year	$ 95
Purchase obligation, due in fifth year	96
Purchase obligation, due after fifth year	$ 298

Minimum amount of purchase arrangement maturing after the fifth fiscal year following the latest fiscal year. Includes, but not limited to, recorded and unrecorded purchase obligations, long-term purchase commitments, and short-term purchase commitments.

No definition available.

Name:	us-gaap_PurchaseObligationDueAfterFifthYear
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant