Debt (Letter of Credit) (Details) - USD ($) $ in Millions |
Mar. 31, 2019 |
Dec. 31, 2018 |
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|---|---|---|---|---|---|---|---|---|---|
| Line of Credit Facility [Line Items] | |||||||||
| Letters of Credit Outstanding, Amount | $ 1,201 | $ 1,365 | |||||||
| Revolving Credit Facility [Member] | |||||||||
| Line of Credit Facility [Line Items] | |||||||||
| Letters of Credit Outstanding, Amount | [1] | 537 | 693 | ||||||
| CDH [Member] | |||||||||
| Line of Credit Facility [Line Items] | |||||||||
| Letters of Credit Outstanding, Amount | [2] | 225 | 251 | ||||||
| Various Project Financing Facilities [Member] | |||||||||
| Line of Credit Facility [Line Items] | |||||||||
| Letters of Credit Outstanding, Amount | 243 | 228 | |||||||
| Other Corporate Facilities [Member] | |||||||||
| Line of Credit Facility [Line Items] | |||||||||
| Letters of Credit Outstanding, Amount | [3] | $ 196 | $ 193 | ||||||
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