Schedule of Financial Instrument and Derivative Offsetting (Details) - USD ($) $ in Millions	Mar. 31, 2016	Dec. 31, 2015
Offsetting Derivative Assets
Gross Derivative Assets	$ 40.1	$ 49.8
Derivative Liabilities Offsetting Derivative Assets in Balance Sheet	0.0	0.0
Net Derivative Assets Reported in Balance Sheet	40.1	49.8
Securities Received as Collateral on Derivative Assets	(13.1)	(12.8)
Cash Collateral from Counterparties	(27.0)	(36.4)
Derivative Assets Net of Collateral	0.0	0.6
Offsetting Securities Borrowed
Gross Securities Borrowed	194.3	181.6
Liabilities Offsetting Securities Borrowed in Balance Sheet	0.0	0.0
Net Securities Borrowed Reported in Balance Sheet	194.3	181.6
Securities Received as Collateral on Securities Borrowed	(145.5)	(152.6)
Cash Received as Collateral on Securities Borrowed	(48.8)	(29.0)
Securities Borrowed Net of Collateral	0.0	0.0
Offsetting of Derivative Assets and Securities Borrowed
Gross Financial Assets	234.4	231.4
Financial Liabilities Offsetting Financial Assets in Balance Sheet	0.0	0.0
Net Financial Assets Reported in Balance Sheet	234.4	231.4
Securities Received as Collateral on Financial Assets	(158.6)	(165.4)
Cash Received as Collateral on Financial Assets	(75.8)	(65.4)
Financial Assets Net of Collateral	0.0	0.6
Offsetting Derivative Liabilities
Net Derivative Liabilities Reported in Balance Sheet	151.2	137.8
Cash Collateral to Counterparties	0.0	0.0
Offsetting Securities Loaned
Gross Securities Loaned	48.8	29.0
Assets Offsetting Securities Loaned in Balance Sheet	0.0	0.0
Net Securities Loaned Reported in Balance Sheet	48.8	29.0
Securities Given as Collateral on Securities Loaned	(48.8)	(29.0)
Cash Given as Collateral on Securities Loaned	0.0	0.0
Securities Loaned Net of Collateral	0.0	0.0
Derivative Liabilities and Securities Lending Liabilities
Gross Financial Liability	106.8	79.2
Financial Assets Offsetting Financial Liabilities in Balance Sheet	0.0	0.0
Net Financial Liabilities Reported in Balance Sheet	106.8	79.2
Securities Given as Collateral on Financial Liabilities	(90.0)	(64.6)
Cash Given as Collateral on Financial Liabilities	0.0	0.0
Financial Liabilities Net of Collateral	16.8	14.6
Over the Counter
Offsetting Derivative Liabilities
Gross Derivative Liability	58.0	50.2
Derivative Assets Offsetting Derivative Liabilities in Balance Sheet	0.0	0.0
Net Derivative Liabilities Reported in Balance Sheet	58.0	50.2
Securities Given as Collateral on Derivative Liabilities	(41.2)	(35.6)
Cash Collateral to Counterparties	0.0	0.0
Derivative Liabilities Net of Collateral	$ 16.8	$ 14.6