Contingencies and Commitments (Details) (USD $)	3 Months Ended
	Mar. 31, 2014 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	$ 24,000,000
Contingent Contractual Obligations [Line Items]
Amount	564,000,000
Number of agreements	35
Guarantees [Member]
Contingent Contractual Obligations [Line Items]
Amount	434,000,000
Number of agreements	21
Maximum exposure range for each agreement	<$1 - 53
Maximum exposure range, lower limit (less than $1)	1,000,000
Maximum exposure range, upper limit	53,000,000
Cash Collateralized Letters Of Credit [Member]
Contingent Contractual Obligations [Line Items]
Amount	129,000,000
Number of agreements	12
Maximum exposure range for each agreement	<$1 - 85
Maximum exposure range, lower limit (less than $1)	1,000,000
Maximum exposure range, upper limit	85,000,000
Letters of credit under secured credit facility [Member]
Contingent Contractual Obligations [Line Items]
Amount	1,000,000
Number of agreements	2
Maximum exposure range for each agreement	<$1
Maximum exposure range, lower limit (less than $1)	$ 1,000,000
Letters of credit under secured credit facility [Member] | Minimum [Member]
Contingent Contractual Obligations [Line Items]
Letter of credit fee percentage paid	0.20%
Letters of credit under secured credit facility [Member] | Maximum [Member]
Contingent Contractual Obligations [Line Items]
Letter of credit fee percentage paid	2.50%