Schedule 2 - Parent Company Financial Statements - Balance Sheets (Details) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
ASSETS
Investments in Subsidiaries	$ 190.6	$ 184.8
Fixed Maturities at Fair Value (Amortized Cost: 2015 – $15.1; 2014 – $12.2)	4,852.3	4,777.6
Fair Value Option Investments	164.5	53.3
Short-term Investments	255.7	342.2
Cash	161.7	76.1	$ 66.5	$ 96.3
Other Receivables	193.2	187.0
Current and Deferred Income Taxes	41.4	0.0
Other Assets	238.5	220.2
Total Assets	8,036.1	7,833.4
LIABILITIES AND SHAREHOLDERS’ EQUITY
Notes Payable	750.6	752.1
Liabilities for Income Taxes	3.8	36.5
Accrued Expenses and Other Liabilities	472.4	409.6
Total Liabilities	6,043.7	5,742.7
Shareholders’ Equity:
Additional Paid-in Capital	654.0	660.1
Retained Earnings	1,209.0	1,202.7
Accumulated Other Comprehensive Income	124.3	222.7
Total Shareholders’ Equity	1,992.4	2,090.7	2,051.5	2,161.7
Total Liabilities and Shareholders’ Equity	8,036.1	7,833.4
Parent Company [Member]
ASSETS
Investments in Subsidiaries	2,586.6	2,677.5
Fixed Maturities at Fair Value (Amortized Cost: 2015 – $15.1; 2014 – $12.2)	15.1	12.2
Equity Securities at Fair Value (Cost: 2015 – $6.4; 2014 – $21.9)	10.9	21.8
Fair Value Option Investments	164.5	53.3
Short-term Investments	134.8	225.1
Cash	15.9	17.9	$ 20.8	$ 2.2
Other Receivables	5.7	6.9
Current and Deferred Income Taxes	0.0	4.7
Other Assets	6.1	5.6
Total Assets	2,939.6	3,025.0
LIABILITIES AND SHAREHOLDERS’ EQUITY
Liabilities for Income Taxes	33.3	14.5
Liabilities for Benefit Plans	154.8	160.2
Accrued Expenses and Other Liabilities	8.5	7.5
Total Liabilities	947.2	934.3
Shareholders’ Equity:
Common Stock	5.1	5.2
Additional Paid-in Capital	654.0	660.1
Retained Earnings	1,209.0	1,202.7
Accumulated Other Comprehensive Income	124.3	222.7
Total Shareholders’ Equity	1,992.4	2,090.7
Total Liabilities and Shareholders’ Equity	2,939.6	3,025.0
Parent Company [Member] | Senior Notes, 6% Due May 15, 2017 [Member]
LIABILITIES AND SHAREHOLDERS’ EQUITY
Notes Payable	359.1	358.5
Parent Company [Member] | Senior Notes, 6% Due November 30, 2015 [Member]
LIABILITIES AND SHAREHOLDERS’ EQUITY
Notes Payable	0.0	249.5
Parent Company [Member] | Senior Notes, 4.35 Percent Due February 15, 2025 [Member]
LIABILITIES AND SHAREHOLDERS’ EQUITY
Notes Payable	247.4	0.0
Parent Company [Member] | Subordinated Debenture, 7.375 Percent Due 2054 [Member]
LIABILITIES AND SHAREHOLDERS’ EQUITY
Notes Payable	144.1	144.1
Senior Notes [Member] | Senior Notes, 6% Due May 15, 2017 [Member]
LIABILITIES AND SHAREHOLDERS’ EQUITY
Notes Payable	359.1	358.5
Senior Notes [Member] | Senior Notes, 6% Due November 30, 2015 [Member]
LIABILITIES AND SHAREHOLDERS’ EQUITY
Notes Payable	0.0	249.5
Senior Notes [Member] | Senior Notes, 4.35 Percent Due February 15, 2025 [Member]
LIABILITIES AND SHAREHOLDERS’ EQUITY
Notes Payable	$ 247.4	$ 0.0