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Summary of Significant Accounting Policies (Tables) | 12 Months Ended
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Dec. 31, 2013
Accounting Policies [Abstract] |
Straight-Line Depreciation Rates | Provisions at composite straight-line depreciation rates approximate the following percentages for the cost of depreciable property:
|  | 2013 |  | 2012 |  | 2011 |  |
| Electric | 2.7% |  | 2.9% |  | 3.2% |  |
| Gas | 1.7% |  | 1.7% |  | 1.6% |  |
| Nonregulated | 2.3% |  | 2.3% |  | 2.3% |  |

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- Definition Tabular disclosure of composite straight-line depreciation rates by segment. + References No definition available. + Details
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