Contingencies and Commitments (Details) $ in Millions		6 Months Ended
		Jun. 30, 2015 USD ($) agreement	Dec. 31, 2013 USD ($)
Loss Contingencies [Line Items]
Regulatory Liabilities			$ 269
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
Obligations made by the Parent Company associated with non-recourse debt		$ 18
Contingent Contractual Obligations [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted		$ 496
Number of Agreements | agreement		28
Guarantee Obligations [Member]
Contingent Contractual Obligations [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted		$ 359
Number of Agreements | agreement		14
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
Number 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		$ 61
Number of Agreements | agreement		7
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		$ 49
Number of Agreements | agreement		6
Loss Contingency, Range of Possible Loss, Minimum		$ 1
Loss Contingency, Range of Possible Loss, Maximum		$ 30
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%

[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.