Fair Value (Details) (USD $) | Sep. 30, 2013 | Dec. 31, 2012 |
In Millions, unless otherwise specified |
Assets [Abstract] | | |
Nuclear decommissioning trusts | ($1,139) | ($1,037) |
Liabilities [Abstract] | | |
Derivative Liabilities, Current | 58 | 125 |
Derivative Liabilities, Noncurrent | 21 | 26 |
Fair Value, Measurements, Recurring [Member] | | |
Assets [Abstract] | | |
Cash and Cash Equivalents, Fair Value Disclosure | -68 | -123 |
Nuclear decommissioning trusts | -1,139 | -1,037 |
Other investments | -124 | -110 |
Derivative assets [Abstract] | | |
Derivative Assets | -98 | -147 |
Assets, Fair Value Disclosure | -1,429 | -1,417 |
Liabilities [Abstract] | | |
Interest Rate Derivative Liabilities, at Fair Value | 0 | 1 |
Derivative Liabilities | 79 | 151 |
Financial and Nonfinancial Liabilities, Fair Value Disclosure | 1,350 | 1,266 |
Fair Value, Measurements, Recurring [Member] | Natural Gas Commodity Contract [Member] | | |
Derivative assets [Abstract] | | |
Derivative Assets | -9 | -40 |
Liabilities [Abstract] | | |
Derivative Liabilities | 26 | 56 |
Fair Value, Measurements, Recurring [Member] | Electricity [Member] | | |
Derivative assets [Abstract] | | |
Derivative Assets | -82 | -102 |
Liabilities [Abstract] | | |
Derivative Liabilities | 51 | 93 |
Fair Value, Measurements, Recurring [Member] | Other Commodity Contract [Member] | | |
Derivative assets [Abstract] | | |
Derivative Assets | -7 | -5 |
Liabilities [Abstract] | | |
Derivative Liabilities | 2 | 1 |
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | | |
Assets [Abstract] | | |
Cash and Cash Equivalents, Fair Value Disclosure | 0 | 0 |
Nuclear decommissioning trusts | -757 | -694 |
Other investments | -76 | -66 |
Derivative assets [Abstract] | | |
Derivative Assets | -436 | -561 |
Assets, Fair Value Disclosure | -1,269 | -1,321 |
Liabilities [Abstract] | | |
Interest Rate Derivative Liabilities, at Fair Value | 0 | 0 |
Derivative Liabilities | 426 | 532 |
Financial and Nonfinancial Liabilities, Fair Value Disclosure | 843 | 789 |
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Natural Gas Commodity Contract [Member] | | |
Derivative assets [Abstract] | | |
Derivative Assets | -388 | -555 |
Liabilities [Abstract] | | |
Derivative Liabilities | 374 | 526 |
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Electricity [Member] | | |
Derivative assets [Abstract] | | |
Derivative Assets | 0 | 0 |
Liabilities [Abstract] | | |
Derivative Liabilities | 0 | 0 |
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Other Commodity Contract [Member] | | |
Derivative assets [Abstract] | | |
Derivative Assets | -48 | -6 |
Liabilities [Abstract] | | |
Derivative Liabilities | 52 | 6 |
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | | |
Assets [Abstract] | | |
Cash and Cash Equivalents, Fair Value Disclosure | -68 | -123 |
Nuclear decommissioning trusts | -382 | -343 |
Other investments | -48 | -44 |
Derivative assets [Abstract] | | |
Derivative Assets | -280 | -295 |
Assets, Fair Value Disclosure | -778 | -805 |
Liabilities [Abstract] | | |
Interest Rate Derivative Liabilities, at Fair Value | 0 | 1 |
Derivative Liabilities | 258 | 315 |
Financial and Nonfinancial Liabilities, Fair Value Disclosure | 520 | 490 |
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Natural Gas Commodity Contract [Member] | | |
Derivative assets [Abstract] | | |
Derivative Assets | -61 | -66 |
Liabilities [Abstract] | | |
Derivative Liabilities | 49 | 73 |
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Electricity [Member] | | |
Derivative assets [Abstract] | | |
Derivative Assets | -210 | -226 |
Liabilities [Abstract] | | |
Derivative Liabilities | 204 | 240 |
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Other Commodity Contract [Member] | | |
Derivative assets [Abstract] | | |
Derivative Assets | -9 | -3 |
Liabilities [Abstract] | | |
Derivative Liabilities | 5 | 1 |
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | | |
Assets [Abstract] | | |
Cash and Cash Equivalents, Fair Value Disclosure | 0 | 0 |
Nuclear decommissioning trusts | 0 | 0 |
Other investments | 0 | 0 |
Derivative assets [Abstract] | | |
Derivative Assets | -127 | -160 |
Assets, Fair Value Disclosure | -127 | -160 |
Liabilities [Abstract] | | |
Interest Rate Derivative Liabilities, at Fair Value | 0 | 0 |
Derivative Liabilities | 131 | 173 |
Financial and Nonfinancial Liabilities, Fair Value Disclosure | -4 | -13 |
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Natural Gas Commodity Contract [Member] | | |
Derivative assets [Abstract] | | |
Derivative Assets | -34 | -24 |
Liabilities [Abstract] | | |
Derivative Liabilities | 48 | 62 |
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Electricity [Member] | | |
Derivative assets [Abstract] | | |
Derivative Assets | -88 | -134 |
Liabilities [Abstract] | | |
Derivative Liabilities | 83 | 111 |
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Other Commodity Contract [Member] | | |
Derivative assets [Abstract] | | |
Derivative Assets | -5 | -2 |
Liabilities [Abstract] | | |
Derivative Liabilities | 0 | 0 |
Fair Value, Measurements, Recurring [Member] | Netting [Member] | | |
Assets [Abstract] | | |
Cash and Cash Equivalents, Fair Value Disclosure | 0 | 0 |
Nuclear decommissioning trusts | 0 | 0 |
Other investments | 0 | 0 |
Derivative assets [Abstract] | | |
Derivative Assets | -745 | -869 |
Assets, Fair Value Disclosure | -745 | -869 |
Liabilities [Abstract] | | |
Interest Rate Derivative Liabilities, at Fair Value | 0 | 0 |
Derivative Liabilities | 736 | 869 |
Financial and Nonfinancial Liabilities, Fair Value Disclosure | 9 | 0 |
Fair Value, Measurements, Recurring [Member] | Netting [Member] | Natural Gas Commodity Contract [Member] | | |
Derivative assets [Abstract] | | |
Derivative Assets | -474 | -605 |
Liabilities [Abstract] | | |
Derivative Liabilities | 445 | 605 |
Fair Value, Measurements, Recurring [Member] | Netting [Member] | Electricity [Member] | | |
Derivative assets [Abstract] | | |
Derivative Assets | -216 | -258 |
Liabilities [Abstract] | | |
Derivative Liabilities | 236 | 258 |
Fair Value, Measurements, Recurring [Member] | Netting [Member] | Other Commodity Contract [Member] | | |
Derivative assets [Abstract] | | |
Derivative Assets | -55 | -6 |
Liabilities [Abstract] | | |
Derivative Liabilities | 55 | 6 |
Current Asset [Member] | Fair Value, Measurements, Recurring [Member] | | |
Derivative assets [Abstract] | | |
Assets, Fair Value Disclosure | -140 | -231 |
Current Asset [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | | |
Derivative assets [Abstract] | | |
Assets, Fair Value Disclosure | -400 | -493 |
Current Asset [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | | |
Derivative assets [Abstract] | | |
Assets, Fair Value Disclosure | -285 | -372 |
Current Asset [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | | |
Derivative assets [Abstract] | | |
Assets, Fair Value Disclosure | -94 | -120 |
Current Asset [Member] | Fair Value, Measurements, Recurring [Member] | Netting [Member] | | |
Derivative assets [Abstract] | | |
Assets, Fair Value Disclosure | -639 | -754 |
Non Current Asset [Member] | Fair Value, Measurements, Recurring [Member] | | |
Derivative assets [Abstract] | | |
Assets, Fair Value Disclosure | -1,289 | -1,186 |
Non Current Asset [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | | |
Derivative assets [Abstract] | | |
Assets, Fair Value Disclosure | -869 | -828 |
Non Current Asset [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | | |
Derivative assets [Abstract] | | |
Assets, Fair Value Disclosure | -493 | -433 |
Non Current Asset [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | | |
Derivative assets [Abstract] | | |
Assets, Fair Value Disclosure | -33 | -40 |
Non Current Asset [Member] | Fair Value, Measurements, Recurring [Member] | Netting [Member] | | |
Derivative assets [Abstract] | | |
Assets, Fair Value Disclosure | -106 | -115 |
Current Liability [Member] | Fair Value, Measurements, Recurring [Member] | | |
Liabilities [Abstract] | | |
Derivative Liabilities, Current | 58 | 125 |
Current Liability [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | | |
Liabilities [Abstract] | | |
Derivative Liabilities, Current | 379 | 466 |
Current Liability [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | | |
Liabilities [Abstract] | | |
Derivative Liabilities, Current | 189 | 269 |
Current Liability [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | | |
Liabilities [Abstract] | | |
Derivative Liabilities, Current | 100 | 144 |
Current Liability [Member] | Fair Value, Measurements, Recurring [Member] | Netting [Member] | | |
Liabilities [Abstract] | | |
Derivative Liabilities, Current | 610 | 754 |
Noncurrent Liability [Member] | Fair Value, Measurements, Recurring [Member] | | |
Liabilities [Abstract] | | |
Derivative Liabilities, Noncurrent | 21 | 26 |
Noncurrent Liability [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | | |
Liabilities [Abstract] | | |
Derivative Liabilities, Noncurrent | 47 | 66 |
Noncurrent Liability [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | | |
Liabilities [Abstract] | | |
Derivative Liabilities, Noncurrent | 69 | 46 |
Noncurrent Liability [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | | |
Liabilities [Abstract] | | |
Derivative Liabilities, Noncurrent | 31 | 29 |
Noncurrent Liability [Member] | Fair Value, Measurements, Recurring [Member] | Netting [Member] | | |
Liabilities [Abstract] | | |
Derivative Liabilities, Noncurrent | 126 | 115 |
Other Investments [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | | |
Assets [Abstract] | | |
Cash and Cash Equivalents, Fair Value Disclosure | -17 | -14 |
Other Investments [Member] | Equity [Member] | Fair Value, Measurements, Recurring [Member] | | |
Assets [Abstract] | | |
Other investments | ($124) | ($110) |