Investment Securities (Fixed maturity investment gains and losses) (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2014		Dec. 31, 2013
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading Securities Gross Unrealized Gain	$ 142.7		$ 133.7
Trading Securities Gross Unrealized Loss	(6.7)		(9.3)
Carrying value	1,743.6		1,700.9
U.S. Government and agency obligations
Schedule of Trading Securities and Other Trading Assets [Line Items]
Cost or amortized cost	209.9		131.0
Trading Securities Gross Unrealized Gain	0.2		0.2
Trading Securities Gross Unrealized Loss	0		(0.1)
Net foreign currency losses	0		0
Carrying value	210.1	[1]	131.1	[1]
Debt securities issued by corporations
Schedule of Trading Securities and Other Trading Assets [Line Items]
Cost or amortized cost	741.2		741.7
Trading Securities Gross Unrealized Gain	14.8		14.1
Trading Securities Gross Unrealized Loss	(0.3)		(1.3)
Net foreign currency losses	0		0
Carrying value	755.7	[1]	754.5	[1]
Municipal obligations
Schedule of Trading Securities and Other Trading Assets [Line Items]
Cost or amortized cost	32.1		16.9
Trading Securities Gross Unrealized Gain	0.2		0
Trading Securities Gross Unrealized Loss	(0.2)		(0.4)
Net foreign currency losses	0		0
Carrying value	32.1	[1]	16.5	[1]
Mortgage-backed and asset-backed securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Cost or amortized cost	881.8		951.5
Trading Securities Gross Unrealized Gain	1.7		1.2
Trading Securities Gross Unrealized Loss	(2.2)		(3.2)
Net foreign currency losses	0		0
Carrying value	881.3	[1]	949.5	[1]
Foreign government obligations
Schedule of Trading Securities and Other Trading Assets [Line Items]
Cost or amortized cost	2.0		2.0
Trading Securities Gross Unrealized Gain	0.3		0.3
Trading Securities Gross Unrealized Loss	0		0
Net foreign currency losses	0		0
Carrying value	2.3	[1]	2.3	[1]
Preferred stocks
Schedule of Trading Securities and Other Trading Assets [Line Items]
Cost or amortized cost	78.3		78.3
Trading Securities Gross Unrealized Gain	6.0		5.0
Trading Securities Gross Unrealized Loss	0		0
Net foreign currency losses	0		0
Carrying value	84.3	[1]	83.3	[1]
Total fixed maturity investments
Schedule of Trading Securities and Other Trading Assets [Line Items]
Cost or amortized cost	1,945.3	[1]	1,921.4	[1]
Trading Securities Gross Unrealized Gain	23.2	[1]	20.8	[1]
Trading Securities Gross Unrealized Loss	(2.7)	[1]	(5.0)	[1]
Net foreign currency losses	0	[1]	0	[1]
Carrying value	$ 1,965.8	[1]	$ 1,937.2	[1]

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