Fair Value Measurements - Narrative (Details) - USD ($) $ in Millions	Mar. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Spread on US Treasury rate for determining discount rate for fair value of deposit liabilities	0.38%	0.265%	0.295%
Carrying Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other investments - structured transactions	$ 141.5	$ 141.3	$ 354.4

The Other investments balance disclosed within the Fair Value Measurements tables exclude certain structured transactions including certain investments in project finance transactions, a payment obligation and liquidity financing provided to a structured credit vehicle as a part of a third party medium term note facility.

No definition available.

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant