Debt (Letter of Credit) (Details) - USD ($) $ in Millions |
Mar. 31, 2016 |
Dec. 31, 2015 |
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|---|---|---|---|---|
| Line of Credit Facility [Line Items] | ||||
| Letters of Credit Outstanding, Amount | $ 754 | $ 755 | ||
| Corporate Revolving Credit Facility [Member] | ||||
| Line of Credit Facility [Line Items] | ||||
| Letters of Credit Outstanding, Amount | [1] | 314 | 316 | |
| CDH [Member] | ||||
| Line of Credit Facility [Line Items] | ||||
| Letters of Credit Outstanding, Amount | 262 | 241 | ||
| Various Project Financing Facilities [Member] | ||||
| Line of Credit Facility [Line Items] | ||||
| Letters of Credit Outstanding, Amount | $ 178 | $ 198 | ||
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