13. Fair Value of Financial Instruments (Details 2) (USD $) In Millions, unless otherwise specified	3 Months Ended	9 Months Ended	3 Months Ended	9 Months Ended	3 Months Ended	9 Months Ended	3 Months Ended	9 Months Ended	3 Months Ended	9 Months Ended	3 Months Ended	9 Months Ended	3 Months Ended	9 Months Ended	3 Months Ended	9 Months Ended	3 Months Ended	9 Months Ended	3 Months Ended	9 Months Ended	3 Months Ended	9 Months Ended	3 Months Ended	9 Months Ended	3 Months Ended	9 Months Ended	3 Months Ended	9 Months Ended	3 Months Ended	9 Months Ended	3 Months Ended	9 Months Ended	3 Months Ended	9 Months Ended	3 Months Ended	9 Months Ended	3 Months Ended	9 Months Ended	3 Months Ended	9 Months Ended	3 Months Ended	9 Months Ended	3 Months Ended	9 Months Ended
	Sep. 30, 2012 U.S. government and agency [Member]	Sep. 30, 2012 U.S. government and agency [Member]	Sep. 30, 2011 U.S. government and agency [Member] As restated and amended [Member]	Sep. 30, 2011 U.S. government and agency [Member] As restated and amended [Member]	Sep. 30, 2012 State and political subdivision [Member]	Sep. 30, 2012 State and political subdivision [Member]	Sep. 30, 2011 State and political subdivision [Member] As restated and amended [Member]	Sep. 30, 2011 State and political subdivision [Member] As restated and amended [Member]	Sep. 30, 2012 Foreign government [Member]	Sep. 30, 2012 Foreign government [Member]	Sep. 30, 2011 Foreign government [Member] As restated and amended [Member]	Sep. 30, 2011 Foreign government [Member] As restated and amended [Member]	Sep. 30, 2012 Corporate [Member]	Sep. 30, 2012 Corporate [Member]	Sep. 30, 2011 Corporate [Member] As restated and amended [Member]	Sep. 30, 2011 Corporate [Member] As restated and amended [Member]	Sep. 30, 2012 Commercial mortgage-backed (CMBS) [Member]	Sep. 30, 2012 Commercial mortgage-backed (CMBS) [Member]	Sep. 30, 2011 Commercial mortgage-backed (CMBS) [Member] As restated and amended [Member]	Sep. 30, 2011 Commercial mortgage-backed (CMBS) [Member] As restated and amended [Member]	Sep. 30, 2012 Residential mortgage-backed (RMBS) [Member]	Sep. 30, 2012 Residential mortgage-backed (RMBS) [Member]	Sep. 30, 2011 Residential mortgage-backed (RMBS) [Member] As restated and amended [Member]	Sep. 30, 2011 Residential mortgage-backed (RMBS) [Member] As restated and amended [Member]	Sep. 30, 2012 CDO/CLO [Member]	Sep. 30, 2012 CDO/CLO [Member]	Sep. 30, 2011 CDO/CLO [Member] As restated and amended [Member]	Sep. 30, 2011 CDO/CLO [Member] As restated and amended [Member]	Sep. 30, 2012 Other asset-backed [Member]	Sep. 30, 2012 Other asset-backed [Member]	Sep. 30, 2011 Other asset-backed [Member] As restated and amended [Member]	Sep. 30, 2011 Other asset-backed [Member] As restated and amended [Member]	Sep. 30, 2012 Available-for-sale equity securities [Member]	Sep. 30, 2012 Available-for-sale equity securities [Member]	Sep. 30, 2011 Available-for-sale equity securities [Member] As restated and amended [Member]	Sep. 30, 2011 Available-for-sale equity securities [Member] As restated and amended [Member]	Sep. 30, 2012 Fair value option investments [Member]	Sep. 30, 2012 Fair value option investments [Member]	Sep. 30, 2011 Fair value option investments [Member] As restated and amended [Member]	Sep. 30, 2011 Fair value option investments [Member] As restated and amended [Member]	Sep. 30, 2012 Total assets [Member]	Sep. 30, 2012 Total assets [Member]	Sep. 30, 2011 Total assets [Member] As restated and amended [Member]	Sep. 30, 2011 Total assets [Member] As restated and amended [Member]
Level 3 Financial Assets:
Fair Value, Total assets, Balance, beginning of period	$ 322.9	$ 336.2	$ 331.7	$ 341.4	$ 181.7	$ 116.6	$ 74.1	$ 67.1	$ 52.9	$ 51.8	$ 46.0	$ 47.1	$ 3,702.2	$ 3,501.5	$ 3,276.7	$ 3,278.3	$ 99.2	$ 100.6	$ 89.2	$ 91.7	$ 857.5	$ 944.2	$ 1,022.9	$ 919.1	$ 207.6	$ 232.4	$ 230.5	$ 238.0	$ 297.5	$ 335.5	$ 357.1	$ 252.8	$ 36.0	$ 29.4	$ 39.9	$ 36.2	$ 159.3	$ 144.8	$ 143.4	$ 126.0	$ 5,916.8	$ 5,793.0	$ 5,611.5	$ 5,397.7
Purchases	0.6	2.6		5.2	10.2	40.5		10.0		5.0			88.4	457.6	26.9	308.1			8.9	5.0	3.8	2.9	44.0	184.4		9.9	10.1	0.3	3.5	17.2	7.8	102.9		5.6		4.0	1.8	26.3		13.6	108.3	567.6	97.7	633.5
Sales	(2.3)	(13.9)	(2.1)	(7.9)	(0.4)	(2.5)	(0.7)	(1.4)		(0.1)			(10.2)	(65.8)	(16.4)	(51.7)		(8.2)	(2.0)	(5.0)	(9.1)	(94.6)	(38.9)	(77.2)	(5.5)	(18.6)	(3.7)	(6.2)	(5.9)	(26.4)	(10.0)	(30.9)					(10.2)	(9.0)	(1.0)	(10.5)	(43.6)	(239.1)	(74.8)	(190.8)
Transfers into Level 3				6.9		22.2	2.5							56.3	175.0	149.0		12.1		8.4									32.5	0.1		3.2		4.8	1.1	0.6					32.5	95.5	178.6	168.1
Transfers out of Level 3						(8.3)						(7.0)	(18.8)	(122.4)	(7.2)	(95.9)		(37.1)		(17.8)										(11.4)		(6.0)					(1.4)				(20.2)	(179.2)	(7.2)	(126.7)
Realized (gains) losses included in income	0.2	0.2												(0.5)	(2.6)	(7.0)		(4.2)	(2.5)	(1.9)	(0.4)	(6.7)	(1.7)	(3.1)	0.5	1.3	(1.2)	(0.8)	(0.5)	(1.5)	(0.3)	0.5	(1.5)	(1.5)			14.6	2.0	(29.8)	7.7	12.9	(10.9)	(13.9)	(4.6)
Unrealized (gains) losses included in other comprehensive loss	(0.8)	(4.5)	22.5	6.5	1.4	24.4	16.9	17.1	2.1	(1.7)	(7.1)	(1.2)	(28.4)	(93.5)	(1.6)	(130.0)	(25.5)	10.5	(9.8)	3.4	(19.0)	(13.0)	(46.4)	(43.3)	13.9	(8.5)	(20.3)	(15.9)	(6.1)	7.5	(10.4)	21.7	(5.2)	(9.0)	(3.4)	(3.2)					(67.6)	(87.8)	(59.6)	(144.9)
Fair Value, Total assets, Balance	$ 282.8	$ 320.6	$ 352.1	$ 352.1	$ 85.7	$ 192.9	$ 92.8	$ 92.8	$ 10.1	$ 55.0	$ 38.9	$ 38.9	$ 2,825.9	$ 3,733.2	$ 3,450.8	$ 3,450.8	$ 73.7	$ 73.7	$ 83.8	$ 83.8	$ 832.8	$ 832.8	$ 979.9	$ 979.9	$ 18.0	$ 216.5	$ 215.4	$ 215.4	$ 41.9	$ 321.0	$ 344.2	$ 344.2	$ 29.3	$ 29.3	$ 37.6	$ 37.6	$ 4.8	$ 164.1	$ 136.8	$ 136.8	$ 5,939.1	$ 5,939.1	$ 5,732.3	$ 5,732.3