Contingencies and Commitments (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2015 agreement
Guarantees Letters Of Credit [Abstract]
The range of expiration dates of guarantees made by the Parent Company	less than one year to more than 20 years
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	525
Number of Agreements	32
Guarantees and commitments
Contingent Contractual Obligations [Line Items]
Amount	365
Number of Agreements	15
Maximum Exposure Range for Each Agreement	$1 — 53
Maximum exposure range, upper limit	53
Maximum Exposure range, lower limit	1
Asset sale related indemnities(1)
Contingent Contractual Obligations [Line Items]
Amount	27	[1]
Number of Agreements	1	[1]
Maximum Exposure Range for Each Agreement	27	[1]
Maximum exposure range, upper limit	27
Maximum Exposure range, lower limit	27
Cash collateralized letters of credit
Contingent Contractual Obligations [Line Items]
Amount	72
Number of Agreements	9
Maximum Exposure Range for Each Agreement	<$1 — 44
Maximum exposure range, lower limit (less than $1)	1
Maximum exposure range, upper limit	44
Letters of credit under the senior secured credit facility
Contingent Contractual Obligations [Line Items]
Amount	61
Number of Agreements	7
Maximum Exposure Range for Each Agreement	<$1 — 29
Maximum exposure range, lower limit (less than $1)	1
Maximum exposure range, upper limit	$ 29
Letters of credit under the senior secured credit facility | Minimum [Member]
Contingent Contractual Obligations [Line Items]
Letter of credit fee percentage paid	0.20%
Letters of credit under the senior secured credit facility | Maximum [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.