Off-Balance Sheet Guarantees and Long Term Standby Purchase Commitments - Long Term Standby Purchase Commitments (Details) (Long-Term Standby Purchase Commitments [Member], USD $)	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014
Long-term Purchase Commitment [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted	$ 2,200,000,000		$ 2,200,000,000
Weighted average remaining maturity, Loans underlying guarantees not held by transferor	14 years 3 months 18 days	14 years 3 months 18 days
Guarantee obligations issued after January 1, 2003 [Member]
Long-term Purchase Commitment [Line Items]
Guarantor Obligations, Current Carrying Value	$ 26,200,000		$ 26,800,000