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Commitments, Guarantees and Contingencies - Clean Water Act and Regulation of Waste Disposal (Details) $ in Millions | 12 Months Ended |
--- | --- | ---
Dec. 31, 2016 USD ($) | Dec. 31, 2015 | Apr. 19, 2013 option
Loss Contingencies [Line Items] |  |  |
Number of treatment options | option |  |  | 8
Number of preferred treatment options | option |  |  | 4
Renewal cycle of waste water discharge permit | 5 years |  |
Clean Water Act |  |  |
Loss Contingencies [Line Items] |  |  |
Annual percentage that fish impingement should be reduced to, per CWA | 12.00% |  |
TMDL limit development period | 5 years |  |
Regulation of Waste Disposal |  |  |
Loss Contingencies [Line Items] |  |  |
Accrual for environmental loss contingencies | $ 137 |  |
Environmental liabilities former gas facilities | 89 |  |
Bond closure and post closure period |  | 45 years |
Period of time to implement plan |  | 12 years |
Minimum | Clean Water Act |  |  |
Loss Contingencies [Line Items] |  |  |
Maximum capital investment required to install technology to meet TDS and Sulfate limits | 150 |  |
Maximum | Clean Water Act |  |  |
Loss Contingencies [Line Items] |  |  |
Maximum capital investment required to install technology to meet TDS and Sulfate limits | $ 300 |  |

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