Debt - Subsidiary Non-recourse Debt in Default or Accelerated (Details) $ in Millions	Mar. 31, 2016 USD ($)
Nonrecourse Debt Default [Line Items]
Materiality threshold for cash distribution from business to Parent	20.00%
Debt Default Amount	$ 695
Maritza [Member]
Nonrecourse Debt Default [Line Items]
Net Assets	719
Kavarna [Member]
Nonrecourse Debt Default [Line Items]
Net Assets	83
Sogrinsk [Domain]
Nonrecourse Debt Default [Line Items]
Net Assets	8
Covenant Violation [Member] | Maritza [Member]
Nonrecourse Debt Default [Line Items]
Debt Default, Short-term Debt, Amount	551
Covenant Violation [Member] | Kavarna [Member]
Nonrecourse Debt Default [Line Items]
Debt Default, Short-term Debt, Amount	138
Covenant Violation [Member] | Sogrinsk [Domain]
Nonrecourse Debt Default [Line Items]
Debt Default, Short-term Debt, Amount	$ 6