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Fair Value of Financial Assets and Liabilities, Derivative Assets and Liabilities at Fair Value (Details) - USD ($)
$ in Thousands
Dec. 31, 2015
Dec. 31, 2014
Derivatives, Fair Value [Line Items]    
Derivative Asset, Collateral, Obligation to Return Cash, Offset $ 0 $ 0
Derivative Liability, Collateral, Right to Reclaim Cash, Offset 4,300 6,600
Other Current Assets [Member]    
Derivatives, Fair Value [Line Items]    
Derivative Asset, Fair Value, Gross Asset 33,842 85,723
Other Noncurrent Assets [Member]    
Derivatives, Fair Value [Line Items]    
Derivative Asset, Fair Value, Gross Asset 51,083 53,775
Other Current Liabilities [Member]    
Derivatives, Fair Value [Line Items]    
Derivative Liability, Fair Value, Gross Liability 29,839 21,632
Other Noncurrent Liabilities [Member]    
Derivatives, Fair Value [Line Items]    
Derivative Liability, Fair Value, Gross Liability 168,311 183,936
Fair Value Measured on a Recurring Basis | Other Current Assets [Member]    
Derivatives, Fair Value [Line Items]    
Derivative Asset, Fair Value, Gross Asset 23,756 67,600
Fair Value Measured on a Recurring Basis | Other Current Assets [Member] | Other Derivative Instruments | Commodity Trading    
Derivatives, Fair Value [Line Items]    
Derivative Asset, Fair Value, Gross Asset 6,230 15,818
Fair Value Measured on a Recurring Basis | Other Current Assets [Member] | Other Derivative Instruments | Electric Commodity    
Derivatives, Fair Value [Line Items]    
Derivative Asset, Fair Value, Gross Asset 17,333 51,423
Fair Value Measured on a Recurring Basis | Other Current Assets [Member] | Other Derivative Instruments | Natural Gas Commodity    
Derivatives, Fair Value [Line Items]    
Derivative Asset, Fair Value, Gross Asset 193 359
Fair Value Measured on a Recurring Basis | Other Noncurrent Assets [Member]    
Derivatives, Fair Value [Line Items]    
Derivative Asset, Fair Value, Gross Asset 20,861 13,466
Fair Value Measured on a Recurring Basis | Other Noncurrent Assets [Member] | Other Derivative Instruments | Commodity Trading    
Derivatives, Fair Value [Line Items]    
Derivative Asset, Fair Value, Gross Asset 20,861 13,466
Fair Value Measured on a Recurring Basis | Other Current Liabilities [Member] | Designated as Hedging Instrument | Vehicle Fuel And Other Commodity | Cash Flow Hedges    
Derivatives, Fair Value [Line Items]    
Derivative Liability, Fair Value, Gross Liability 205 118
Fair Value Measured on a Recurring Basis | Other Current Liabilities [Member] | Other Derivative Instruments    
Derivatives, Fair Value [Line Items]    
Derivative Liability, Fair Value, Gross Liability 6,978 645
Fair Value Measured on a Recurring Basis | Other Current Liabilities [Member] | Other Derivative Instruments | Commodity Trading    
Derivatives, Fair Value [Line Items]    
Derivative Liability, Fair Value, Gross Liability 1,669 0
Fair Value Measured on a Recurring Basis | Other Current Liabilities [Member] | Other Derivative Instruments | Electric Commodity    
Derivatives, Fair Value [Line Items]    
Derivative Liability, Fair Value, Gross Liability 0 0
Fair Value Measured on a Recurring Basis | Other Current Liabilities [Member] | Other Derivative Instruments | Natural Gas Commodity    
Derivatives, Fair Value [Line Items]    
Derivative Liability, Fair Value, Gross Liability 5,104 527
Fair Value Measured on a Recurring Basis | Other Noncurrent Liabilities [Member] | Designated as Hedging Instrument | Vehicle Fuel And Other Commodity | Cash Flow Hedges    
Derivatives, Fair Value [Line Items]    
Derivative Liability, Fair Value, Gross Liability   102
Fair Value Measured on a Recurring Basis | Other Noncurrent Liabilities [Member] | Other Derivative Instruments    
Derivatives, Fair Value [Line Items]    
Derivative Liability, Fair Value, Gross Liability 10,118 994
Fair Value Measured on a Recurring Basis | Other Noncurrent Liabilities [Member] | Other Derivative Instruments | Commodity Trading    
Derivatives, Fair Value [Line Items]    
Derivative Liability, Fair Value, Gross Liability 10,118 857
Fair Value Measured on a Recurring Basis | Other Noncurrent Liabilities [Member] | Other Derivative Instruments | Natural Gas Commodity    
Derivatives, Fair Value [Line Items]    
Derivative Liability, Fair Value, Gross Liability   35
Fair Value Measured on a Recurring Basis | Level 1 | Other Current Assets [Member]    
Derivatives, Fair Value [Line Items]    
Derivative Asset, Fair Value, Gross Asset 225 0
Fair Value Measured on a Recurring Basis | Level 1 | Other Current Assets [Member] | Other Derivative Instruments | Commodity Trading    
Derivatives, Fair Value [Line Items]    
Derivative Asset, Fair Value, Gross Asset 225 0
Fair Value Measured on a Recurring Basis | Level 1 | Other Current Assets [Member] | Other Derivative Instruments | Electric Commodity    
Derivatives, Fair Value [Line Items]    
Derivative Asset, Fair Value, Gross Asset 0 0
Fair Value Measured on a Recurring Basis | Level 1 | Other Current Assets [Member] | Other Derivative Instruments | Natural Gas Commodity    
Derivatives, Fair Value [Line Items]    
Derivative Asset, Fair Value, Gross Asset 0 0
Fair Value Measured on a Recurring Basis | Level 1 | Other Noncurrent Assets [Member]    
Derivatives, Fair Value [Line Items]    
Derivative Asset, Fair Value, Gross Asset 0 0
Fair Value Measured on a Recurring Basis | Level 1 | Other Noncurrent Assets [Member] | Other Derivative Instruments | Commodity Trading    
Derivatives, Fair Value [Line Items]    
Derivative Asset, Fair Value, Gross Asset 0 0
Fair Value Measured on a Recurring Basis | Level 1 | Other Current Liabilities [Member] | Designated as Hedging Instrument | Vehicle Fuel And Other Commodity | Cash Flow Hedges    
Derivatives, Fair Value [Line Items]    
Derivative Liability, Fair Value, Gross Liability 0 0
Fair Value Measured on a Recurring Basis | Level 1 | Other Current Liabilities [Member] | Other Derivative Instruments    
Derivatives, Fair Value [Line Items]    
Derivative Liability, Fair Value, Gross Liability 152 0
Fair Value Measured on a Recurring Basis | Level 1 | Other Current Liabilities [Member] | Other Derivative Instruments | Commodity Trading    
Derivatives, Fair Value [Line Items]    
Derivative Liability, Fair Value, Gross Liability 152 0
Fair Value Measured on a Recurring Basis | Level 1 | Other Current Liabilities [Member] | Other Derivative Instruments | Electric Commodity    
Derivatives, Fair Value [Line Items]    
Derivative Liability, Fair Value, Gross Liability 0 0
Fair Value Measured on a Recurring Basis | Level 1 | Other Current Liabilities [Member] | Other Derivative Instruments | Natural Gas Commodity    
Derivatives, Fair Value [Line Items]    
Derivative Liability, Fair Value, Gross Liability 0 0
Fair Value Measured on a Recurring Basis | Level 1 | Other Noncurrent Liabilities [Member] | Designated as Hedging Instrument | Vehicle Fuel And Other Commodity | Cash Flow Hedges    
Derivatives, Fair Value [Line Items]    
Derivative Liability, Fair Value, Gross Liability   0
Fair Value Measured on a Recurring Basis | Level 1 | Other Noncurrent Liabilities [Member] | Other Derivative Instruments    
Derivatives, Fair Value [Line Items]    
Derivative Liability, Fair Value, Gross Liability 0 0
Fair Value Measured on a Recurring Basis | Level 1 | Other Noncurrent Liabilities [Member] | Other Derivative Instruments | Commodity Trading    
Derivatives, Fair Value [Line Items]    
Derivative Liability, Fair Value, Gross Liability 0 0
Fair Value Measured on a Recurring Basis | Level 1 | Other Noncurrent Liabilities [Member] | Other Derivative Instruments | Natural Gas Commodity    
Derivatives, Fair Value [Line Items]    
Derivative Liability, Fair Value, Gross Liability   0
Fair Value Measured on a Recurring Basis | Level 2 | Other Current Assets [Member]    
Derivatives, Fair Value [Line Items]    
Derivative Asset, Fair Value, Gross Asset 11,116 14,707
Fair Value Measured on a Recurring Basis | Level 2 | Other Current Assets [Member] | Other Derivative Instruments | Commodity Trading    
Derivatives, Fair Value [Line Items]    
Derivative Asset, Fair Value, Gross Asset 10,620 14,326
Fair Value Measured on a Recurring Basis | Level 2 | Other Current Assets [Member] | Other Derivative Instruments | Electric Commodity    
Derivatives, Fair Value [Line Items]    
Derivative Asset, Fair Value, Gross Asset 0 0
Fair Value Measured on a Recurring Basis | Level 2 | Other Current Assets [Member] | Other Derivative Instruments | Natural Gas Commodity    
Derivatives, Fair Value [Line Items]    
Derivative Asset, Fair Value, Gross Asset 496 381
Fair Value Measured on a Recurring Basis | Level 2 | Other Noncurrent Assets [Member]    
Derivatives, Fair Value [Line Items]    
Derivative Asset, Fair Value, Gross Asset 27,416 17,617
Fair Value Measured on a Recurring Basis | Level 2 | Other Noncurrent Assets [Member] | Other Derivative Instruments | Commodity Trading    
Derivatives, Fair Value [Line Items]    
Derivative Asset, Fair Value, Gross Asset 27,416 17,617
Fair Value Measured on a Recurring Basis | Level 2 | Other Current Liabilities [Member] | Designated as Hedging Instrument | Vehicle Fuel And Other Commodity | Cash Flow Hedges    
Derivatives, Fair Value [Line Items]    
Derivative Liability, Fair Value, Gross Liability 205 118
Fair Value Measured on a Recurring Basis | Level 2 | Other Current Liabilities [Member] | Other Derivative Instruments    
Derivatives, Fair Value [Line Items]    
Derivative Liability, Fair Value, Gross Liability 13,478 8,640
Fair Value Measured on a Recurring Basis | Level 2 | Other Current Liabilities [Member] | Other Derivative Instruments | Commodity Trading    
Derivatives, Fair Value [Line Items]    
Derivative Liability, Fair Value, Gross Liability 7,866 7,974
Fair Value Measured on a Recurring Basis | Level 2 | Other Current Liabilities [Member] | Other Derivative Instruments | Electric Commodity    
Derivatives, Fair Value [Line Items]    
Derivative Liability, Fair Value, Gross Liability 0 0
Fair Value Measured on a Recurring Basis | Level 2 | Other Current Liabilities [Member] | Other Derivative Instruments | Natural Gas Commodity    
Derivatives, Fair Value [Line Items]    
Derivative Liability, Fair Value, Gross Liability 5,407 548
Fair Value Measured on a Recurring Basis | Level 2 | Other Noncurrent Liabilities [Member] | Designated as Hedging Instrument | Vehicle Fuel And Other Commodity | Cash Flow Hedges    
Derivatives, Fair Value [Line Items]    
Derivative Liability, Fair Value, Gross Liability   102
Fair Value Measured on a Recurring Basis | Level 2 | Other Noncurrent Liabilities [Member] | Other Derivative Instruments    
Derivatives, Fair Value [Line Items]    
Derivative Liability, Fair Value, Gross Liability 19,898 7,027
Fair Value Measured on a Recurring Basis | Level 2 | Other Noncurrent Liabilities [Member] | Other Derivative Instruments | Commodity Trading    
Derivatives, Fair Value [Line Items]    
Derivative Liability, Fair Value, Gross Liability 19,898 6,890
Fair Value Measured on a Recurring Basis | Level 2 | Other Noncurrent Liabilities [Member] | Other Derivative Instruments | Natural Gas Commodity    
Derivatives, Fair Value [Line Items]    
Derivative Liability, Fair Value, Gross Liability   35
Fair Value Measured on a Recurring Basis | Level 3 | Other Current Assets [Member]    
Derivatives, Fair Value [Line Items]    
Derivative Asset, Fair Value, Gross Asset 22,671 67,557
Fair Value Measured on a Recurring Basis | Level 3 | Other Current Assets [Member] | Other Derivative Instruments | Commodity Trading    
Derivatives, Fair Value [Line Items]    
Derivative Asset, Fair Value, Gross Asset 1,250 4,732
Fair Value Measured on a Recurring Basis | Level 3 | Other Current Assets [Member] | Other Derivative Instruments | Electric Commodity    
Derivatives, Fair Value [Line Items]    
Derivative Asset, Fair Value, Gross Asset 21,421 62,825
Fair Value Measured on a Recurring Basis | Level 3 | Other Current Assets [Member] | Other Derivative Instruments | Natural Gas Commodity    
Derivatives, Fair Value [Line Items]    
Derivative Asset, Fair Value, Gross Asset 0 0
Fair Value Measured on a Recurring Basis | Level 3 | Other Noncurrent Assets [Member]    
Derivatives, Fair Value [Line Items]    
Derivative Asset, Fair Value, Gross Asset 0 0
Fair Value Measured on a Recurring Basis | Level 3 | Other Noncurrent Assets [Member] | Other Derivative Instruments | Commodity Trading    
Derivatives, Fair Value [Line Items]    
Derivative Asset, Fair Value, Gross Asset 0 0
Fair Value Measured on a Recurring Basis | Level 3 | Other Current Liabilities [Member] | Designated as Hedging Instrument | Vehicle Fuel And Other Commodity | Cash Flow Hedges    
Derivatives, Fair Value [Line Items]    
Derivative Liability, Fair Value, Gross Liability 0 0
Fair Value Measured on a Recurring Basis | Level 3 | Other Current Liabilities [Member] | Other Derivative Instruments    
Derivatives, Fair Value [Line Items]    
Derivative Liability, Fair Value, Gross Liability 4,643 11,402
Fair Value Measured on a Recurring Basis | Level 3 | Other Current Liabilities [Member] | Other Derivative Instruments | Commodity Trading    
Derivatives, Fair Value [Line Items]    
Derivative Liability, Fair Value, Gross Liability 555 0
Fair Value Measured on a Recurring Basis | Level 3 | Other Current Liabilities [Member] | Other Derivative Instruments | Electric Commodity    
Derivatives, Fair Value [Line Items]    
Derivative Liability, Fair Value, Gross Liability 4,088 11,402
Fair Value Measured on a Recurring Basis | Level 3 | Other Current Liabilities [Member] | Other Derivative Instruments | Natural Gas Commodity    
Derivatives, Fair Value [Line Items]    
Derivative Liability, Fair Value, Gross Liability 0 0
Fair Value Measured on a Recurring Basis | Level 3 | Other Noncurrent Liabilities [Member] | Designated as Hedging Instrument | Vehicle Fuel And Other Commodity | Cash Flow Hedges    
Derivatives, Fair Value [Line Items]    
Derivative Liability, Fair Value, Gross Liability   0
Fair Value Measured on a Recurring Basis | Level 3 | Other Noncurrent Liabilities [Member] | Other Derivative Instruments    
Derivatives, Fair Value [Line Items]    
Derivative Liability, Fair Value, Gross Liability 0 0
Fair Value Measured on a Recurring Basis | Level 3 | Other Noncurrent Liabilities [Member] | Other Derivative Instruments | Commodity Trading    
Derivatives, Fair Value [Line Items]    
Derivative Liability, Fair Value, Gross Liability 0 0
Fair Value Measured on a Recurring Basis | Level 3 | Other Noncurrent Liabilities [Member] | Other Derivative Instruments | Natural Gas Commodity    
Derivatives, Fair Value [Line Items]    
Derivative Liability, Fair Value, Gross Liability   0
Fair Value Measured on a Recurring Basis | Fair Value Total | Other Current Assets [Member]    
Derivatives, Fair Value [Line Items]    
Derivative Asset, Fair Value, Gross Asset 34,012 82,264
Fair Value Measured on a Recurring Basis | Fair Value Total | Other Current Assets [Member] | Other Derivative Instruments | Commodity Trading    
Derivatives, Fair Value [Line Items]    
Derivative Asset, Fair Value, Gross Asset 12,095 19,058
Fair Value Measured on a Recurring Basis | Fair Value Total | Other Current Assets [Member] | Other Derivative Instruments | Electric Commodity    
Derivatives, Fair Value [Line Items]    
Derivative Asset, Fair Value, Gross Asset 21,421 62,825
Fair Value Measured on a Recurring Basis | Fair Value Total | Other Current Assets [Member] | Other Derivative Instruments | Natural Gas Commodity    
Derivatives, Fair Value [Line Items]    
Derivative Asset, Fair Value, Gross Asset 496 381
Fair Value Measured on a Recurring Basis | Fair Value Total | Other Noncurrent Assets [Member]    
Derivatives, Fair Value [Line Items]    
Derivative Asset, Fair Value, Gross Asset 27,416 17,617
Fair Value Measured on a Recurring Basis | Fair Value Total | Other Noncurrent Assets [Member] | Other Derivative Instruments | Commodity Trading    
Derivatives, Fair Value [Line Items]    
Derivative Asset, Fair Value, Gross Asset 27,416 17,617
Fair Value Measured on a Recurring Basis | Fair Value Total | Other Current Liabilities [Member] | Designated as Hedging Instrument | Vehicle Fuel And Other Commodity | Cash Flow Hedges    
Derivatives, Fair Value [Line Items]    
Derivative Liability, Fair Value, Gross Liability 205 118
Fair Value Measured on a Recurring Basis | Fair Value Total | Other Current Liabilities [Member] | Other Derivative Instruments    
Derivatives, Fair Value [Line Items]    
Derivative Liability, Fair Value, Gross Liability 18,273 20,042
Fair Value Measured on a Recurring Basis | Fair Value Total | Other Current Liabilities [Member] | Other Derivative Instruments | Commodity Trading    
Derivatives, Fair Value [Line Items]    
Derivative Liability, Fair Value, Gross Liability 8,573 7,974
Fair Value Measured on a Recurring Basis | Fair Value Total | Other Current Liabilities [Member] | Other Derivative Instruments | Electric Commodity    
Derivatives, Fair Value [Line Items]    
Derivative Liability, Fair Value, Gross Liability 4,088 11,402
Fair Value Measured on a Recurring Basis | Fair Value Total | Other Current Liabilities [Member] | Other Derivative Instruments | Natural Gas Commodity    
Derivatives, Fair Value [Line Items]    
Derivative Liability, Fair Value, Gross Liability 5,407 548
Fair Value Measured on a Recurring Basis | Fair Value Total | Other Noncurrent Liabilities [Member] | Designated as Hedging Instrument | Vehicle Fuel And Other Commodity | Cash Flow Hedges    
Derivatives, Fair Value [Line Items]    
Derivative Liability, Fair Value, Gross Liability   102
Fair Value Measured on a Recurring Basis | Fair Value Total | Other Noncurrent Liabilities [Member] | Other Derivative Instruments    
Derivatives, Fair Value [Line Items]    
Derivative Liability, Fair Value, Gross Liability 19,898 7,027
Fair Value Measured on a Recurring Basis | Fair Value Total | Other Noncurrent Liabilities [Member] | Other Derivative Instruments | Commodity Trading    
Derivatives, Fair Value [Line Items]    
Derivative Liability, Fair Value, Gross Liability 19,898 6,890
Fair Value Measured on a Recurring Basis | Fair Value Total | Other Noncurrent Liabilities [Member] | Other Derivative Instruments | Natural Gas Commodity    
Derivatives, Fair Value [Line Items]    
Derivative Liability, Fair Value, Gross Liability   35
Fair Value Measured on a Recurring Basis | Netting | Other Current Assets [Member]    
Derivatives, Fair Value [Line Items]    
Derivative Asset, Fair Value, Gross Asset (10,256) [1] (14,664) [2]
Fair Value Measured on a Recurring Basis | Netting | Other Current Assets [Member] | Other Derivative Instruments | Commodity Trading    
Derivatives, Fair Value [Line Items]    
Derivative Asset, Fair Value, Gross Asset (5,865) [1] (3,240) [2]
Fair Value Measured on a Recurring Basis | Netting | Other Current Assets [Member] | Other Derivative Instruments | Electric Commodity    
Derivatives, Fair Value [Line Items]    
Derivative Asset, Fair Value, Gross Asset (4,088) [1] (11,402) [2]
Fair Value Measured on a Recurring Basis | Netting | Other Current Assets [Member] | Other Derivative Instruments | Natural Gas Commodity    
Derivatives, Fair Value [Line Items]    
Derivative Asset, Fair Value, Gross Asset (303) [1] (22) [2]
Fair Value Measured on a Recurring Basis | Netting | Other Noncurrent Assets [Member]    
Derivatives, Fair Value [Line Items]    
Derivative Asset, Fair Value, Gross Asset (6,555) [1] (4,151) [2]
Fair Value Measured on a Recurring Basis | Netting | Other Noncurrent Assets [Member] | Other Derivative Instruments | Commodity Trading    
Derivatives, Fair Value [Line Items]    
Derivative Asset, Fair Value, Gross Asset (6,555) [1] (4,151) [2]
Fair Value Measured on a Recurring Basis | Netting | Other Current Liabilities [Member] | Designated as Hedging Instrument | Vehicle Fuel And Other Commodity | Cash Flow Hedges    
Derivatives, Fair Value [Line Items]    
Derivative Liability, Fair Value, Gross Liability 0 [1] 0 [2]
Fair Value Measured on a Recurring Basis | Netting | Other Current Liabilities [Member] | Other Derivative Instruments    
Derivatives, Fair Value [Line Items]    
Derivative Liability, Fair Value, Gross Liability (11,295) [1] (19,397) [2]
Fair Value Measured on a Recurring Basis | Netting | Other Current Liabilities [Member] | Other Derivative Instruments | Commodity Trading    
Derivatives, Fair Value [Line Items]    
Derivative Liability, Fair Value, Gross Liability (6,904) [1] (7,974) [2]
Fair Value Measured on a Recurring Basis | Netting | Other Current Liabilities [Member] | Other Derivative Instruments | Electric Commodity    
Derivatives, Fair Value [Line Items]    
Derivative Liability, Fair Value, Gross Liability (4,088) [1] (11,402) [2]
Fair Value Measured on a Recurring Basis | Netting | Other Current Liabilities [Member] | Other Derivative Instruments | Natural Gas Commodity    
Derivatives, Fair Value [Line Items]    
Derivative Liability, Fair Value, Gross Liability (303) [1] (21) [2]
Fair Value Measured on a Recurring Basis | Netting | Other Noncurrent Liabilities [Member] | Designated as Hedging Instrument | Vehicle Fuel And Other Commodity | Cash Flow Hedges    
Derivatives, Fair Value [Line Items]    
Derivative Liability, Fair Value, Gross Liability [2]   0
Fair Value Measured on a Recurring Basis | Netting | Other Noncurrent Liabilities [Member] | Other Derivative Instruments    
Derivatives, Fair Value [Line Items]    
Derivative Liability, Fair Value, Gross Liability (9,780) [1] (6,033) [2]
Fair Value Measured on a Recurring Basis | Netting | Other Noncurrent Liabilities [Member] | Other Derivative Instruments | Commodity Trading    
Derivatives, Fair Value [Line Items]    
Derivative Liability, Fair Value, Gross Liability (9,780) [1] (6,033) [2]
Fair Value Measured on a Recurring Basis | Netting | Other Noncurrent Liabilities [Member] | Other Derivative Instruments | Natural Gas Commodity    
Derivatives, Fair Value [Line Items]    
Derivative Liability, Fair Value, Gross Liability [2]   0
Fair Value, Measurements, Nonrecurring [Member] | Other Current Assets [Member] | Purchased Power Agreements    
Derivatives, Fair Value [Line Items]    
Derivative Asset, Fair Value, Gross Asset 10,086 [3] 18,123 [4]
Fair Value, Measurements, Nonrecurring [Member] | Other Noncurrent Assets [Member] | Purchased Power Agreements    
Derivatives, Fair Value [Line Items]    
Derivative Asset, Fair Value, Gross Asset 30,222 [3] 40,309 [4]
Fair Value, Measurements, Nonrecurring [Member] | Other Current Liabilities [Member] | Purchased Power Agreements    
Derivatives, Fair Value [Line Items]    
Derivative Liability, Fair Value, Gross Liability 22,861 [3] 20,987 [4]
Fair Value, Measurements, Nonrecurring [Member] | Other Noncurrent Liabilities [Member] | Purchased Power Agreements    
Derivatives, Fair Value [Line Items]    
Derivative Liability, Fair Value, Gross Liability $ 158,193 [3] $ 182,942 [4]
[1] Xcel Energy nets derivative instruments and related collateral in its consolidated balance sheet when supported by a legally enforceable master netting agreement, and all derivative instruments and related collateral amounts were subject to master netting agreements at Dec. 31, 2015. At Dec. 31, 2015, derivative assets and liabilities include no obligations to return cash collateral and rights to reclaim cash collateral of $4.3 million. The counterparty netting amounts presented exclude settlement receivables and payables and non-derivative amounts that may be subject to the same master netting agreements.
[2] Xcel Energy nets derivative instruments and related collateral in its consolidated balance sheet when supported by a legally enforceable master netting agreement, and all derivative instruments and related collateral amounts were subject to master netting agreements at Dec. 31, 2014. At Dec. 31, 2014, derivative assets and liabilities include no obligations to return cash collateral and rights to reclaim cash collateral of $6.6 million. The counterparty netting amounts presented exclude settlement receivables and payables and non-derivative amounts that may be subject to the same master netting agreements.
[3] In 2003, as a result of implementing new guidance on the normal purchase exception for derivative accounting, Xcel Energy began recording several long-term PPAs at fair value due to accounting requirements related to underlying price adjustments. As these purchases are recovered through normal regulatory recovery mechanisms in the respective jurisdictions, the changes in fair value for these contracts were offset by regulatory assets and liabilities. During 2006, Xcel Energy qualified these contracts under the normal purchase exception. Based on this qualification, the contracts are no longer adjusted to fair value and the previous carrying value of these contracts will be amortized over the remaining contract lives along with the offsetting regulatory assets and liabilities.
[4] In 2003, as a result of implementing new guidance on the normal purchase exception for derivative accounting, Xcel Energy began recording several long-term PPAs at fair value due to accounting requirements related to underlying price adjustments. As these purchases are recovered through normal regulatory recovery mechanisms in the respective jurisdictions, the changes in fair value for these contracts were offset by regulatory assets and liabilities. During 2006, Xcel Energy qualified these contracts under the normal purchase exception. Based on this qualification, the contracts are no longer adjusted to fair value and the previous carrying value of these contracts will be amortized over the remaining contract lives along with the offsetting regulatory assets and liabilities.