Contingencies (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014 agreement
Guarantees Letters Of Credit [Abstract]
Lower limit of expiration dates of guarantees (less than one year)	1 year
Upper limit of expiration dates of guarantees (more than 20 years)	20 years
Obligations made by the Parent Company associated with non-recourse debt	$ 24
Contingent Contractual Obligations [Line Items]
Amount	552
Number of Agreements	31
Parent Company
Contingent Contractual Obligations [Line Items]
Letter Of Credit Fee Range Minimum	0.20%
Letter Of Credit Fee Range Maximum	2.50%
Guarantees and commitments
Contingent Contractual Obligations [Line Items]
Amount	390
Number of Agreements	16
Maximum Exposure Range, Lower Limit	1
Maximum exposure range, upper limit	53
Asset sale related indemnities
Contingent Contractual Obligations [Line Items]
Amount	27
Number of Agreements	1
Maximum exposure range, upper limit	27
Cash collateralized letters of credit
Contingent Contractual Obligations [Line Items]
Amount	74
Number of Agreements	9
Maximum Exposure Range, Lower Limit	1
Maximum exposure range, upper limit	47
Cash collateralized letters of credit | Parent Company
Contingent Contractual Obligations [Line Items]
Amount	74
Letters of credit under the senior secured credit facility
Contingent Contractual Obligations [Line Items]
Number of Agreements	5
Letters of credit outstanding	61
Maximum Exposure Range, Lower Limit	1
Maximum exposure range, upper limit	$ 29