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Fair Value Measurements Fair Value Measurements Using Significant Unobservable Inputs (Details) (USD $) | 3 Months Ended |  |
--- | --- | --- | ---
Dec. 31, 2013 | Dec. 31, 2012 | Sep. 30, 2013 | Sep. 30, 2012
ASSETS |  |  |  |  |
Commodity contract derivatives | $ 4,000,000 |  |  | $ 3,000,000 |
Liabilities |  |  |  |  |
Commodity contract derivatives | 150,000,000 |  |  | 144,000,000 |
Number of contracts | 1 |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Amount of gain (loss) recognized in income | 0 |  |  |  |
Partnership Interest |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Balance | 169,000,000 |  | 66,000,000 | 159,000,000 | 53,000,000
Purchases | 8,000,000 |  | 12,000,000 |  |
Issuances | 0 |  | 0 |  |
Sales | (2,000,000) |  | (1,000,000) |  |
Settlements | 0 |  | 0 |  |
Net unrealized gains (losses) deferred as regulatory assets and liabilities | 4,000,000 |  | 2,000,000 |  |
Commodity Contract Derivatives |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |
Balance | (145,000,000) |  | (224,000,000) | (140,000,000) | (267,000,000)
Purchases | 0 |  | 0 |  |
Issuances | 0 |  | 0 |  |
Sales | 0 |  | 0 |  |
Settlements | 0 |  | 0 |  |
Net unrealized gains (losses) deferred as regulatory assets and liabilities | 5,000,000 |  | 43,000,000 |  |
Maximum |  |  |  |  |
ASSETS |  |  |  |  |
Fair value inputs, counterparty credit risk | 18.00% | [1] |  |  |
Fair value measurements tons per year | 1,000,000,000 |  |  |  |
Price per ton | 85.25 |  |  |  |
Liabilities |  |  |  |  |
Fair value measurements tons per year | 1,000,000,000 |  |  |  |
Price per ton | 85.25 |  |  |  |
Minimum |  |  |  |  |
ASSETS |  |  |  |  |
Fair value inputs, counterparty credit risk | 18.00% | [1] |  |  |
Fair value measurements tons per year | 900,000,000 |  |  |  |
Price per ton | 11.90 |  |  |  |
Liabilities |  |  |  |  |
Fair value measurements tons per year | 900,000,000 |  |  |  |
Price per ton | 11.90 |  |  |  |
Fair Value, Inputs, Level 3 |  |  |  |  |
ASSETS |  |  |  |  |
Commodity contract derivatives | 4,000,000 |  |  | 3,000,000 |
Liabilities |  |  |  |  |
Commodity contract derivatives | $ 149,000,000 |  |  | $ 143,000,000 |
[1] | Applies to only one contract.

X
- Definition The fair value as of the balance sheet date of firm obligations in physical commodity contracts (for example, agricultural products, metals and energy). + References No definition available. + Details
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- Definition This item represents the amount of the total realized and unrealized gains or losses for the period which are deferred as regulatory assets and liabilities; the fair value of which assets or liabilities was or is measured on a recurring basis using significant unobservable inputs (Level 3). + References No definition available. + Details
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- Definition The fair value measurement of tons per year used to determine fair value + References No definition available. + Details
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- Definition Issues that have taken place during the period in relation to assets or liabilities measured at fair value and categorized within Level 3 of the fair value hierarchy. + References No definition available. + Details
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- Definition Purchases that have taken place during the period in relation to assets or liabilities measured at fair value and categorized within Level 3 of the fair value hierarchy. + References No definition available. + Details
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- Definition Sales that have taken place during the period in relation to assets or liabilities measured at fair value and categorized within Level 3 of the fair value hierarchy. + References No definition available. + Details
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- Definition Settlements that have taken place during the period in relation to assets or liabilities measured at fair value and categorized within Level 3 of the fair value hierarchy. + References No definition available. + Details
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- Definition This element represents an asset or liability measured at fair value using significant unobservable inputs (Level 3) which is required for reconciliation purposes of beginning and ending balances. + References No definition available. + Details
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- Definition The price per ton used for the determination of fair value. + References No definition available. + Details
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- Definition Amount of increase (decrease) in the fair value of derivatives recognized in the income statement. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 4A -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=7476318&loc=SL5618551-113959 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 4C -Subparagraph (a),(c),(d),(e) -URI http://asc.fasb.org/extlink&oid=7476318&loc=SL5624171-113959 + Details
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- Definition Risk that one party to the contract will default expressed as a percentage, used as an input to measure fair value. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (bbb) -URI http://asc.fasb.org/extlink&oid=25499696&loc=d3e19207-110258 + Details
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- Definition The fair value as of the balance sheet date of firm holdings in physical commodity contracts (for example, agricultural products, metals and energy). Includes both pledged (to counterparties as collateral for financing transactions) and unpledged holdings. + References No definition available. + Details
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