Off-Balance Sheet Guarantees and Long Term Standby Purchase Commitments - Long Term Standby Purchase Commitments (Details) - Long-Term Standby Purchase Commitments [Member] - USD ($) $ in Millions	6 Months Ended	12 Months Ended
	Jun. 30, 2015	Dec. 31, 2014
Long-term Purchase Commitment [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted	$ 2,200.0	$ 2,200.0
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	$ 26.6	$ 26.8