Contingencies and Commitments (Details) (USD $) In Millions, unless otherwise specified	6 Months Ended
	Jun. 30, 2013 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 21 years
Lower limit of expiration dates of guarantees (less than one year)	1 year
Upper limit of expiration dates of guarantees (more than 21 years)	21 years
Obligations made by the Parent Company associated with non-recourse debt	$ 24
Contingent Contractual Obligations [Line Items]
Amount	874
Number of agreements	37
Guarantees [Member]
Contingent Contractual Obligations [Line Items]
Amount	640
Number of agreements	20
Maximum exposure range for each agreement	<$1 - 265
Maximum exposure range, lower limit	1
Maximum exposure range, upper limit	265
Cash Collateralized Letters Of Credit [Member]
Contingent Contractual Obligations [Line Items]
Amount	231
Number of agreements	13
Maximum exposure range for each agreement	$1 - 154
Maximum exposure range, lower limit	1
Maximum exposure range, upper limit	154
Letters of credit under secured credit facility [Member]
Contingent Contractual Obligations [Line Items]
Amount	3
Number of agreements	4
Maximum exposure range for each agreement	<$1 - 2
Maximum exposure range, lower limit	1
Maximum exposure range, upper limit	$ 2
Letters of credit under secured credit facility [Member] | Minimum [Member]
Contingent Contractual Obligations [Line Items]
Letter of credit fees paid	0.25%
Letters of credit under secured credit facility [Member] | Maximum [Member]
Contingent Contractual Obligations [Line Items]
Letter of credit fees paid	3.25%