Investments Unrealized Capital Losses 1 (Details) (USD $) In Millions, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Schedule of Available-for-sale Securities [Line Items]
Six months or less below amortized cost, Unrealized Capital Losses	$ 7.8	$ 50.9
More than six months and twelve months or less below amortized cost, Unrealized Capital Losses	6.4	42.3
More than twelve months below amortized cost, Unrealized Capital Losses	114.3	205.8
Total Unrealized Capital Losses	128.5	299.0
Fair value decline below amortized cost less than 20%
Schedule of Available-for-sale Securities [Line Items]
Six months or less below amortized cost, Amortized Cost	541.4	1,638.7
Six months or less below amortized cost, Unrealized Capital Losses	25.8	52.5
Six months or less below amortized cost, Number of Securities	113	271
More than six months and twelve months or less below amortized cost, Amortized Cost	179.2	645.4
More than six months and twelve months or less below amortized cost, Unrealized Capital Losses	9.9	38.0
More than six months and twelve months or less below amortized cost, Number of Securities	39	67
More than twelve months below amortized cost, Amortized Cost	333.4	735.1
More than twelve months below amortized cost, Unrealized Capital Losses	13.5	47.0
More than twelve months below amortized cost, Number of Securities	85	126
Total Amortized Cost	1,054.0	3,019.2
Total Unrealized Capital Losses	49.2	137.5
Total Number of Securities	237	464
Fair value decline below amortized cost greater than 20%
Schedule of Available-for-sale Securities [Line Items]
Six months or less below amortized cost, Amortized Cost	43.6	178.0
Six months or less below amortized cost, Unrealized Capital Losses	10.4	52.5
Six months or less below amortized cost, Number of Securities	14	49
More than six months and twelve months or less below amortized cost, Amortized Cost	11.8	57.1
More than six months and twelve months or less below amortized cost, Unrealized Capital Losses	3.5	17.3
More than six months and twelve months or less below amortized cost, Number of Securities	8	22
More than twelve months below amortized cost, Amortized Cost	184.6	221.4
More than twelve months below amortized cost, Unrealized Capital Losses	65.4	91.7
More than twelve months below amortized cost, Number of Securities	62	80
Total Amortized Cost	240.0	456.5
Total Unrealized Capital Losses	79.3	161.5
Total Number of Securities	84	151
U.S. corporate, state and municipalities
Schedule of Available-for-sale Securities [Line Items]
Six months or less below amortized cost, Unrealized Capital Losses	2.3	17.6
More than six months and twelve months or less below amortized cost, Unrealized Capital Losses	3.8	4.1
More than twelve months below amortized cost, Unrealized Capital Losses	17.2	20.6
Total Unrealized Capital Losses	23.3	42.3
U.S. corporate, state and municipalities | Fair value decline below amortized cost less than 20%
Schedule of Available-for-sale Securities [Line Items]
Total Amortized Cost	446.9	1,112.3
Total Unrealized Capital Losses	12.2	32.4
Total Number of Securities	67	137
U.S. corporate, state and municipalities | Fair value decline below amortized cost greater than 20%
Schedule of Available-for-sale Securities [Line Items]
Total Amortized Cost	19.5	34.5
Total Unrealized Capital Losses	11.1	9.9
Total Number of Securities	1	5
Foreign
Schedule of Available-for-sale Securities [Line Items]
Six months or less below amortized cost, Unrealized Capital Losses	4.1	30.2
More than six months and twelve months or less below amortized cost, Unrealized Capital Losses	1.5	5.0
More than twelve months below amortized cost, Unrealized Capital Losses	22.3	34.6
Total Unrealized Capital Losses	27.9	69.8
Foreign | Fair value decline below amortized cost less than 20%
Schedule of Available-for-sale Securities [Line Items]
Total Amortized Cost	217.9	850.6
Total Unrealized Capital Losses	10.8	41.7
Total Number of Securities	19	131
Foreign | Fair value decline below amortized cost greater than 20%
Schedule of Available-for-sale Securities [Line Items]
Total Amortized Cost	60.9	86.3
Total Unrealized Capital Losses	17.1	28.1
Total Number of Securities	14	12
Residential mortgage-backed securities
Schedule of Available-for-sale Securities [Line Items]
Six months or less below amortized cost, Unrealized Capital Losses	0.6	0.9
More than six months and twelve months or less below amortized cost, Unrealized Capital Losses	0.6	5.7
More than twelve months below amortized cost, Unrealized Capital Losses	35.4	84.3
Total Unrealized Capital Losses	36.6	90.9
Residential mortgage-backed securities | Fair value decline below amortized cost less than 20%
Schedule of Available-for-sale Securities [Line Items]
Total Amortized Cost	231.4	500.9
Total Unrealized Capital Losses	15.1	31.7
Total Number of Securities	103	98
Residential mortgage-backed securities | Fair value decline below amortized cost greater than 20%
Schedule of Available-for-sale Securities [Line Items]
Total Amortized Cost	72.3	158.4
Total Unrealized Capital Losses	21.5	59.2
Total Number of Securities	45	89
Commercial mortgage-backed securities
Schedule of Available-for-sale Securities [Line Items]
Six months or less below amortized cost, Unrealized Capital Losses	0.8	1.9
More than six months and twelve months or less below amortized cost, Unrealized Capital Losses	0.5	17.9
More than twelve months below amortized cost, Unrealized Capital Losses	3.2	6.6
Total Unrealized Capital Losses	4.5	26.4
Commercial mortgage-backed securities | Fair value decline below amortized cost less than 20%
Schedule of Available-for-sale Securities [Line Items]
Total Amortized Cost	39.2	446.3
Total Unrealized Capital Losses	2.1	25.1
Total Number of Securities	8	24
Commercial mortgage-backed securities | Fair value decline below amortized cost greater than 20%
Schedule of Available-for-sale Securities [Line Items]
Total Amortized Cost	10.1	5.6
Total Unrealized Capital Losses	2.4	1.3
Total Number of Securities	2	1
Other asset-backed securities
Schedule of Available-for-sale Securities [Line Items]
Six months or less below amortized cost, Unrealized Capital Losses	0	0.3
More than six months and twelve months or less below amortized cost, Unrealized Capital Losses	0	9.6
More than twelve months below amortized cost, Unrealized Capital Losses	36.2	59.7
Total Unrealized Capital Losses	36.2	69.6
Other asset-backed securities | Fair value decline below amortized cost less than 20%
Schedule of Available-for-sale Securities [Line Items]
Total Amortized Cost	118.6	109.1
Total Unrealized Capital Losses	9.0	6.6
Total Number of Securities	40	74
Other asset-backed securities | Fair value decline below amortized cost greater than 20%
Schedule of Available-for-sale Securities [Line Items]
Total Amortized Cost	77.2	171.7
Total Unrealized Capital Losses	$ 27.2	$ 63.0
Total Number of Securities	22	44