Fair Value Disclosures (Carrying Value and Fair Value of the Financial Instruments that are Not recognized or are Not Carried at Fair Value) (Details) - Nonrecurring - USD ($) $ in Millions		Jun. 30, 2017	Dec. 31, 2016
Carrying Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Commercial mortgage loans on real estate		$ 624.0	$ 624.0
Policy loans		37.7	38.5
Other investments		42.0	36.3
Total financial assets		703.7	698.8
Policy reserves under investment products (Individual and group annuities, subject to discretionary withdrawal)	[1]	641.6	651.0
Funds withheld under reinsurance		153.4	111.7
Debt		1,136.6	1,067.0
Total financial liabilities		1,931.6	1,829.7
Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Commercial mortgage loans on real estate		635.5	634.9
Policy loans		37.7	38.5
Other investments		42.0	36.3
Total financial assets		715.2	709.7
Policy reserves under investment products (Individual and group annuities, subject to discretionary withdrawal)	[1]	654.0	680.4
Funds withheld under reinsurance		153.4	111.7
Debt		1,246.4	1,159.7
Total financial liabilities		2,053.8	1,951.8
Fair Value | Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Commercial mortgage loans on real estate		0.0	0.0
Policy loans		37.7	38.5
Other investments		0.0	0.0
Total financial assets		37.7	38.5
Policy reserves under investment products (Individual and group annuities, subject to discretionary withdrawal)	[1]	0.0	0.0
Funds withheld under reinsurance		153.4	111.7
Debt		0.0	0.0
Total financial liabilities		153.4	111.7
Fair Value | Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Commercial mortgage loans on real estate		0.0	0.0
Policy loans		0.0	0.0
Other investments		0.0	0.0
Total financial assets		0.0	0.0
Policy reserves under investment products (Individual and group annuities, subject to discretionary withdrawal)	[1]	0.0	0.0
Funds withheld under reinsurance		0.0	0.0
Debt		1,246.4	1,159.7
Total financial liabilities		1,246.4	1,159.7
Fair Value | Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Commercial mortgage loans on real estate		635.5	634.9
Policy loans		0.0	0.0
Other investments		42.0	36.3
Total financial assets		677.5	671.2
Policy reserves under investment products (Individual and group annuities, subject to discretionary withdrawal)	[1]	654.0	680.4
Funds withheld under reinsurance		0.0	0.0
Debt		0.0	0.0
Total financial liabilities		$ 654.0	$ 680.4

[1] Only the fair value of the Company’s policy reserves for investment-type contracts (those without significant mortality or morbidity risk) are reflected in the table above.