| Three Months | |||||||||||||||||||||||
| Ended March 31, 2016 | Years Ended December 31, | ||||||||||||||||||||||
| 2015 | 2014 | 2013 | 2012 | 2011 | |||||||||||||||||||
| Earnings, as defined: | |||||||||||||||||||||||
|     Income (Loss) from Continuing Operations         Before Income Taxes (a) | $ | 257 | $ | (368 | ) | $ | 303 | $ | (420 | ) | $ | 665 | $ | 1,061 | |||||||||
|     Adjustments to reflect earnings from equity         method investments on a cash basis | — | — | — | — | — | 1 | |||||||||||||||||
| 257 | (368 | ) | 303 | (420 | ) | 665 | 1,062 | ||||||||||||||||
| Total fixed charges as below | 68 | 236 | 161 | 226 | 238 | 259 | |||||||||||||||||
|     Less: | |||||||||||||||||||||||
|     Capitalized interest | 7 | 20 | 22 | 35 | 37 | 38 | |||||||||||||||||
|     Interest expense and fixed charges related to         discontinued operations | — | — | 10 | 14 | 12 | 6 | |||||||||||||||||
| Total fixed charges included in Income (Loss) from   Continuing Operations Before Income Taxes | 61 | 216 | 129 | 177 | 189 | 215 | |||||||||||||||||
|     Total earnings | $ | 318 | $ | (152 | ) | $ | 432 | $ | (243 | ) | $ | 854 | $ | 1,277 | |||||||||
| Fixed charges, as defined: | |||||||||||||||||||||||
|     Interest charges | $ | 67 | $ | 231 | $ | 156 | $ | 207 | $ | 214 | $ | 223 | |||||||||||
|     Estimated interest component of operating rentals | 1 | 5 | 5 | 19 | 24 | 36 | |||||||||||||||||
|           Total fixed charges (b) | $ | 68 | $ | 236 | $ | 161 | $ | 226 | $ | 238 | $ | 259 | |||||||||||
| Ratio of earnings to fixed charges (a) | 4.7 | (0.6 | ) | 2.7 | (1.1 | ) | 3.6 | 4.9 | |||||||||||||||
| (a) | The three months ended March 31, 2016 includes $140 million of net pre-tax gains related to the sale of certain generation facilities.  See Note 7 to the Financial Statements for additional information on the sales.   | 
| (b) | Interest on unrecognized tax benefits is not included in fixed charges.  |