Off-Balance Sheet Guarantees and Long Term Standby Purchase Commitments - Narrative (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Long-term Purchase Commitment [Line Items]
Term of Guarantees Minimum	1 year
Term of Guarantees Maximum	30 years
Guarantee obligations issued after January 1, 2003 [Member]
Long-term Purchase Commitment [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted	3,800,000	$ 3,900,000
Guarantee obligations issued prior to January 1, 2003 [Member]
Long-term Purchase Commitment [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted	70,600	$ 108,700