Schedule 2 - Parent Company Financial Statements - Balance Sheets (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
ASSETS
Investments in Subsidiaries	$ 175.9	$ 190.6
Fixed Maturities at Fair Value (Amortized Cost: 2016 – $46.3; 2015 – $15.1)	5,124.9	4,852.3
Fair Value Option Investments	111.4	164.5
Short-term Investments	273.7	255.7
Cash	115.7	161.7	$ 76.1	$ 66.5
Other Receivables	198.6	193.2
Current Income Tax Assets	15.5	9.5
Other Assets	255.9	238.5
Total Assets	8,210.5	8,036.1
LIABILITIES AND SHAREHOLDERS’ EQUITY
Accrued Expenses and Other Liabilities	453.2	472.4
Total Liabilities	6,235.3	6,043.7
Shareholders’ Equity:
Additional Paid-in Capital	660.3	654.0
Retained Earnings	1,172.8	1,209.0
Accumulated Other Comprehensive Income	137.0	124.3
Stockholders' Equity Attributable to Parent	1,975.2	1,992.4	2,090.7	2,051.5
Total Liabilities and Shareholders’ Equity	8,210.5	8,036.1
Parent Company [Member]
ASSETS
Investments in Subsidiaries	2,575.5	2,586.6
Fixed Maturities at Fair Value (Amortized Cost: 2016 – $46.3; 2015 – $15.1)	46.3	15.1
Equity Securities at Fair Value (Cost: 2016 – $5.2; 2015 – $11.1)	5.3	10.9
Fair Value Option Investments	111.4	164.5
Short-term Investments	120.0	134.8
Cash	15.7	15.9	$ 17.9	$ 20.8
Other Receivables	3.4	5.7
Current Income Tax Assets	2.4	0.0
Other Assets	7.5	6.1
Total Assets	2,887.5	2,939.6
LIABILITIES AND SHAREHOLDERS’ EQUITY
Current Income Tax Liability	0.0	11.3
Deferred Income Tax Assets, Net	34.0	22.0
Liabilities for Benefit Plans	118.7	154.8
Accrued Expenses and Other Liabilities	8.0	8.5
Total Liabilities	912.3	947.2
Shareholders’ Equity:
Common Stock	5.1	5.1
Additional Paid-in Capital	660.3	654.0
Retained Earnings	1,172.8	1,209.0
Accumulated Other Comprehensive Income	137.0	124.3
Stockholders' Equity Attributable to Parent	1,975.2	1,992.4
Total Liabilities and Shareholders’ Equity	2,887.5	2,939.6
Parent Company [Member] | Senior Notes, 6% Due May 15, 2017 [Member]
LIABILITIES AND SHAREHOLDERS’ EQUITY
Notes Payable	359.8	359.1
Parent Company [Member] | Senior Notes, 4.35 Percent Due February 15, 2025 [Member]
LIABILITIES AND SHAREHOLDERS’ EQUITY
Notes Payable	247.7	247.4
Parent Company [Member] | Subordinated Debenture, 7.375 Percent Due 2054 [Member]
LIABILITIES AND SHAREHOLDERS’ EQUITY
Notes Payable	$ 144.1	$ 144.1