Contingencies and Commitments - Loss Contingencies (Details) - USD ($) $ in Millions	3 Months Ended
	Jun. 30, 2015	Sep. 30, 2015	Dec. 31, 2014
Eletropaulo [Domain]
Loss Contingencies [Line Items]
Reversal Of Legal Contingency	$ 161
Environmental Remediation Contingency [Domain]
Environmental Contingencies
Liability recorded for projected environmental remediation costs		$ 9	$ 12
Litigation Contingencies
Maximum potential loss		1
Litigation [Member]
Litigation Contingencies
Minimum potential loss		1,000
Maximum potential loss		1,300
Aggregate reserves for claims deemed both probable and reasonably estimable		$ 184	$ 199
Regulated Revenue [Member] | Eletropaulo [Domain]
Loss Contingencies [Line Items]
Reversal Of Legal Contingency	97
Interest Expense [Member] | Eletropaulo [Domain]
Loss Contingencies [Line Items]
Reversal Of Legal Contingency	$ 64