Schedule of Level 3 Financial Assets (Details) (Level 3, USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
U.S. government and agency
Level 3 Financial Assets:
Balance, beginning of period	$ 58.8	$ 25.9
Purchases	24.2	44.3
Sales	(7.5)	(9.1)
Transfers into Level 3	0	0
Transfers out of Level 3	0	0
Realized & unrealized gains (losses) included in income	0	0
Unrealized gains (losses) included in OCI	4.7	(2.3)
Total	80.2	58.8
State and political subdivision
Level 3 Financial Assets:
Balance, beginning of period	133.8	116.1
Purchases	51.2	47.8
Sales	(2.2)	(1.5)
Transfers into Level 3	0	0
Transfers out of Level 3	0	0
Realized & unrealized gains (losses) included in income	0	0
Unrealized gains (losses) included in OCI	10.5	(28.6)
Total	193.3	133.8
Foreign government
Level 3 Financial Assets:
Balance, beginning of period	3.3	8.0
Purchases	2.2	0
Sales	0	0
Transfers into Level 3	10.7	1.6
Transfers out of Level 3	0	(6.1)
Realized & unrealized gains (losses) included in income	0	0
Unrealized gains (losses) included in OCI	(0.1)	(0.2)
Total	16.1	3.3
Corporate
Level 3 Financial Assets:
Balance, beginning of period	1,091.9	797.9
Purchases	335.0	356.4
Sales	(64.6)	(57.0)
Transfers into Level 3	68.5	41.6
Transfers out of Level 3	(44.3)	(10.9)
Realized & unrealized gains (losses) included in income	(0.9)	0.7
Unrealized gains (losses) included in OCI	31.6	(36.8)
Total	1,417.2	1,091.9
CMBS
Level 3 Financial Assets:
Balance, beginning of period	31.9	19.3
Purchases	8.1	19.3
Sales	(6.5)	(1.7)
Transfers into Level 3	33.8	0
Transfers out of Level 3	(6.9)	(1.5)
Realized & unrealized gains (losses) included in income	0.3	(0.2)
Unrealized gains (losses) included in OCI	3.9	(3.3)
Total	64.6	31.9
RMBS
Level 3 Financial Assets:
Balance, beginning of period	176.1	223.3
Purchases	2.3	1.3
Sales	(20.2)	(36.4)
Transfers into Level 3	0	5.1
Transfers out of Level 3	(4.3)	0
Realized & unrealized gains (losses) included in income	0.3	(0.5)
Unrealized gains (losses) included in OCI	(2.6)	(16.7)
Total	151.6	176.1
Collateralized debt obligation (“CDO”) / collateralized loan obligation (“CLO”)
Level 3 Financial Assets:
Balance, beginning of period	70.9	56.8
Purchases	35.2	36.6
Sales	(20.1)	(10.6)
Transfers into Level 3	0	0
Transfers out of Level 3	0	0
Realized & unrealized gains (losses) included in income	0.6	(0.3)
Unrealized gains (losses) included in OCI	(3.1)	(11.6)
Total	83.5	70.9
Other asset-backed (“ABS”)
Level 3 Financial Assets:
Balance, beginning of period	82.3	80.1
Purchases	13.7	13.4
Sales	(17.3)	(10.2)
Transfers into Level 3	1.0	0
Transfers out of Level 3	0	0
Realized & unrealized gains (losses) included in income	0.1	0
Unrealized gains (losses) included in OCI	(1.9)	(1.0)
Total	77.9	82.3
Total available-for-sale debt securities
Level 3 Financial Assets:
Balance, beginning of period	1,649.0	1,327.4
Purchases	471.9	519.1
Sales	(138.4)	(126.5)
Transfers into Level 3	114.0	48.3
Transfers out of Level 3	(55.5)	(18.5)
Realized & unrealized gains (losses) included in income	0.4	(0.3)
Unrealized gains (losses) included in OCI	43.0	(100.5)
Total	2,084.4	1,649.0
Available-for-sale equity securities
Level 3 Financial Assets:
Balance, beginning of period	11.2	3.6
Purchases	17.2	8.4
Sales	0	0
Transfers into Level 3	0	0
Transfers out of Level 3	0	0
Realized & unrealized gains (losses) included in income	0	0
Unrealized gains (losses) included in OCI	0.3	(0.8)
Total	28.7	11.2
Fair value investments
Level 3 Financial Assets:
Balance, beginning of period	35.6	22.7
Purchases	1.0	21.1
Sales	(2.3)	(8.3)
Transfers into Level 3	0	0
Transfers out of Level 3	0	0
Realized & unrealized gains (losses) included in income	(0.6)	0.1
Unrealized gains (losses) included in OCI	0	0
Total	33.7	35.6
Total assets
Level 3 Financial Assets:
Balance, beginning of period	1,695.8	1,353.7
Purchases	490.1	548.6
Sales	(140.7)	(134.8)
Transfers into Level 3	114.0	48.3
Transfers out of Level 3	(55.5)	(18.5)
Realized & unrealized gains (losses) included in income	(0.2)	(0.2)
Unrealized gains (losses) included in OCI	43.3	(101.3)
Total	$ 2,146.8	$ 1,695.8