Contingencies and Commitments (Details) $ in Millions		3 Months Ended
		Mar. 31, 2016 USD ($) agreement	Jun. 30, 2015 USD ($)	Mar. 31, 2015 USD ($)	Dec. 31, 2013 USD ($)
Guarantees Letters Of Credit [Abstract]
The range of expiration dates of guarantees made by the Parent Company		less than one year to more than 19 years
Contingent Contractual Obligations [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted		$ 475
No. of Agreements | agreement		26
Loss Contingency Accrual, Period Increase (Decrease)		$ (1)		$ 14
Guarantee Obligations [Member]
Contingent Contractual Obligations [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted		$ 355
No. of Agreements | agreement		13
Loss Contingency, Range of Possible Loss, Minimum		$ 1
Loss Contingency, Range of Possible Loss, Maximum		53
Indemnification Agreement [Member]
Contingent Contractual Obligations [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted	[1]	$ 27
No. of Agreements | agreement	[1]	1
Loss Contingency, Range of Possible Loss, Minimum	[1]	$ 27
Loss Contingency, Range of Possible Loss, Maximum	[1]	27
Financial Standby Letter of Credit [Member]
Contingent Contractual Obligations [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted		$ 62
No. of Agreements | agreement		9
Loss Contingency, Range of Possible Loss, Minimum		$ 1
Loss Contingency, Range of Possible Loss, Maximum		29
Standby Letters of Credit [Member]
Contingent Contractual Obligations [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted		$ 31
No. of Agreements | agreement		3
Loss Contingency, Range of Possible Loss, Minimum		$ 3
Loss Contingency, Range of Possible Loss, Maximum		$ 15
Minimum [Member] | Standby Letters of Credit [Member]
Contingent Contractual Obligations [Line Items]
Letter of credit fee percentage paid		0.20%
Maximum [Member] | Standby Letters of Credit [Member]
Contingent Contractual Obligations [Line Items]
Letter of credit fee percentage paid		2.50%
Eletropaulo [Domain] | Regulatory Liability [Domain]
Contingent Contractual Obligations [Line Items]
Loss Contingency Accrual, Period Increase (Decrease)			$ 161		$ (269)

[1] (1) Excludes normal and customary representations and warranties in agreements for the sale of assets (including ownership in associated legal entities) where the associated risk is considered to be nominal.