Investments Offsetting for Derivatives and Securities Lending Balances (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Offsetting Derivative Assets [Abstract]
Gross Derivative Asset	$ 10.8	$ 81.6
Derivative Liabilities Offsetting Derivative Assets in Balance Sheet	0	0
Net Derivative Assets Reported in Balance Sheet	10.8	81.6
Securities Received as Collateral on Derivative Assets	(9.5)	(72.9)
Cash collateral from counterparties	(1.1)	0
Derivative Assets Net of Collateral	0.2	8.7
Offsetting Securities Borrowed [Abstract]
Gross Securities Borrowed	201.6	452.8
Liabilities Offsetting Securities Borrowed in Balance Sheet	0	0
Net Securities Borrowed Reported in Balance Sheet	201.6	452.8
Securities Received as Collateral on Securities Borrowed	(125.1)	0
Cash Received as Collateral on Securities Borrowed	(76.5)	(452.8)
Securities Borrowed Net of Collateral	0	0
Offsetting Derivative Asset, Securities Purchased under Agreements to Resell, Securities Borrowed [Abstract]
Derivative Asset, Securities Purchased under Agreements to Resell, Securities Borrowed, Gross	212.4	534.4
Derivative Asset, Securities Purchased under Agreements to Resell, Securities Borrowed, Liability	0	0
Derivative Asset, Securities Purchased under Agreements to Resell, Securities Borrowed	212.4	534.4
Derivative Asset, Securities Purchased under Agreements to Resell, Securities Borrowed, Collateral, Obligation to Return Securities	(134.6)	(72.9)
Derivative Asset, Securities Purchased under Agreements to Resell, Securities Borrowed, Collateral, Obligation to Return Cash	(77.6)	(452.8)
Derivative Asset, Securities Purchased under Agreements to Resell, Securities Borrowed, Amount Offset Against Collateral	0.2	8.7
Offsetting Derivative Liabilities [Abstract]
Derivative Liability, Fair Value, Gross Liability	135.6	170.5
Derivative Liability, Fair Value, Gross Asset	0	0
Derivative Liability, Fair Value, Amount Not Offset Against Collateral	135.6	170.5
Derivative, Collateral, Right to Reclaim Securities	(98.6)	(129.8)
Derivative, Collateral, Right to Reclaim Cash	0	(1.8)
Derivative Liability, Fair Value, Amount Offset Against Collateral	37.0	38.9
Offsetting Securities Loaned [Abstract]
Securities Loaned, Gross	76.5	455.8
Securities Loaned, Asset	0	0
Securities Loaned, Collateral, Right to Reclaim Securities	(76.5)	(452.8)
Securities Loaned, Collateral, Right to Reclaim Cash	0	0
Securities Loaned, Amount Offset Against Collateral	0	3.0
Offsetting Derivative Liability, Securities Sold under Agreements to Resell, Securities Loaned [Abstract]
Derivative Liability, Securities Sold under Agreements to Resell, Securities Loaned, Gross	212.1	626.3
Derivative Liability, Securities Sold under Agreements to Resell, Securities Loaned, Asset	0	0
Derivative Liability, Securities Sold under Agreements to Resell, Securities Loaned	212.1	626.3
Derivative Liability, Securities Sold under Agreements to Resell, Securities Loaned, Collateral, Right to Reclaim Securities	(175.1)	(582.6)
Derivative Liability, Securities Sold under Agreements to Resell, Securities Loaned, Collateral, Right to Reclaim Cash	0	(1.8)
Derivative Liability, Securities Sold under Agreements to Resell, Securities Loaned, Amount Offset Against Collateral	$ 37.0	$ 41.9