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	3 Months Ended	12 Months Ended
	Mar. 31, 2016	Dec. 31, 2015
Long-term Purchase Commitment [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted	$ 2,700.0	$ 2,800.0
Weighted average remaining maturity, Loans underlying guarantees not held by transferor	14 years 7 months 10 days	14 years 7 months 10 days
Guarantee obligations issued after January 1, 2003 [Member]
Long-term Purchase Commitment [Line Items]
Guarantor Obligations, Current Carrying Value	$ 29.9	$ 30.3