Debt - Subsidiary Non-recourse Debt in Default or Accelerated (Details) $ in Millions	Sep. 30, 2015 USD ($)
Nonrecourse Debt Default [Line Items]
Debt Default Amount	$ 1,054
Maritza [Member]
Nonrecourse Debt Default [Line Items]
Net Assets	648
Sul Subsidiary [Member]
Nonrecourse Debt Default [Line Items]
Net Assets	433
Kavarna [Member]
Nonrecourse Debt Default [Line Items]
Net Assets	77
Altai [Domain]
Nonrecourse Debt Default [Line Items]
Net Assets	10
Covenant Violation [Member] | Maritza [Member]
Nonrecourse Debt Default [Line Items]
Debt Default, Short-term Debt, Amount	576
Covenant Violation [Member] | Sul Subsidiary [Member]
Nonrecourse Debt Default [Line Items]
Debt Default, Short-term Debt, Amount	327
Covenant Violation [Member] | Kavarna [Member]
Nonrecourse Debt Default [Line Items]
Debt Default, Short-term Debt, Amount	143
Covenant Violation [Member] | Altai [Domain]
Nonrecourse Debt Default [Line Items]
Debt Default, Short-term Debt, Amount	$ 8