Fair Value Measurement (Details 3) (USD $) In Millions, unless otherwise specified	3 Months Ended				6 Months Ended
	Jun. 30, 2012		Jun. 30, 2011		Jun. 30, 2012		Jun. 30, 2011
Obligations of state and political subdivisions
Fair Value Level 3 Rollforward
Balance at the beginning of the period	$ 9.5				$ 9.5
Total pretax realized and unrealized gains/(losses) recorded in
Net Income (loss)	0.1	[1],[2]			0.3	[1],[2]
Other comprehensive income (loss)	0.1	[1]			0.5	[1]
Purchases	0				0
Settlements	0				(0.6)
Consolidations, Deconsolidations, net	0				0
Balance at the end of the period	9.7				9.7
Total pre-tax realized/unrealized gains/(losses) recorded in
Change in unrealized gains/(losses) related to financial instruments held at the reporting date	0.1				0.5
RMBS
Fair Value Level 3 Rollforward
Balance at the beginning of the period	135.7		210.1		133.6		99.4
Total pretax realized and unrealized gains/(losses) recorded in
Net Income (loss)	4.0	[1],[2]	(35.2)	[1],[2]	4.8	[1],[2]	(31.3)	[1],[2]
Other comprehensive income (loss)	(16.4)	[1]	(16.9)	[1]	(6.5)	[1]	(47.7)	[1]
Purchases	54.4		1.6		54.4		152.2
Sales			(8.0)				(21.0)
Settlements	(11.0)		0		(19.6)		0
Consolidations, Deconsolidations, net	0		(63.6)		0		(63.6)
Balance at the end of the period	166.7		88.0		166.7		88.0
Total pre-tax realized/unrealized gains/(losses) recorded in
Change in unrealized gains/(losses) related to financial instruments held at the reporting date	(16.4)		(16.9)		(6.5)		(47.7)
Asset-backed securities
Fair Value Level 3 Rollforward
Balance at the beginning of the period	258.1		232.1		235.5		210.2
Total pretax realized and unrealized gains/(losses) recorded in
Net Income (loss)	7.8	[1],[2]	2.1	[1],[2]	13.6	[1],[2]	3.7	[1],[2]
Other comprehensive income (loss)	(12.0)	[1]	(7.3)	[1]	(11.9)	[1]	13.0	[1]
Purchases	21.6		47.1		39.6		47.1
Sales			(0.1)				(0.1)
Settlements	(1.5)		0		(2.8)		0
Consolidations, Deconsolidations, net	0		0		0		0
Balance at the end of the period	274.0		273.9		274.0		273.9
Total pre-tax realized/unrealized gains/(losses) recorded in
Change in unrealized gains/(losses) related to financial instruments held at the reporting date	(12.0)		(7.3)		(11.9)		13.0
Other invested assets
Fair Value Level 3 Rollforward
Balance at the beginning of the period	1.6		2.2		1.7		2.3
Total pretax realized and unrealized gains/(losses) recorded in
Net Income (loss)	0	[1]	0	[1]	0	[1]	0	[1]
Other comprehensive income (loss)	(0.2)	[1]	(0.2)	[1]	(0.3)	[1]	(0.3)	[1]
Purchases	0		0		0		0
Sales			0				0
Settlements	0		0		0		0
Consolidations, Deconsolidations, net	0		0		0		0
Balance at the end of the period	1.4		2.0		1.4		2.0
Total pre-tax realized/unrealized gains/(losses) recorded in
Change in unrealized gains/(losses) related to financial instruments held at the reporting date	(0.2)		(0.2)		(0.3)		(0.3)
FG VIEs' assets, at fair value
Fair Value Level 3 Rollforward
Balance at the beginning of the period	2,827.7		3,679.0		2,819.1		3,657.5
Total pretax realized and unrealized gains/(losses) recorded in
Net Income (loss)	42.8	[1],[3]	(211.6)	[1],[3]	177.9	[1],[3]	22.8	[1],[3]
Other comprehensive income (loss)	0	[1]	0	[1]	0	[1]	0	[1]
Purchases	0		0		0		0
Sales			0				0
Settlements	(144.5)		(257.6)		(285.5)		(470.5)
Consolidations, Deconsolidations, net	0		282.4		14.5		282.4
Balance at the end of the period	2,726.0		3,492.2		2,726.0		3,492.2
Total pre-tax realized/unrealized gains/(losses) recorded in
Change in unrealized gains/(losses) related to financial instruments held at the reporting date	72.0		(84.7)		303.4		263.6
Other assets
Fair Value Level 3 Rollforward
Balance at the beginning of the period	39.9				53.8
Total pretax realized and unrealized gains/(losses) recorded in
Net Income (loss)	4.3	[1],[4]			(9.6)	[1],[4]
Other comprehensive income (loss)	0	[1]			0	[1]
Purchases	0				0
Settlements	0				0
Consolidations, Deconsolidations, net	0				0
Balance at the end of the period	44.2				44.2
Total pre-tax realized/unrealized gains/(losses) recorded in
Change in unrealized gains/(losses) related to financial instruments held at the reporting date	4.3				(9.6)
Credit derivative asset (liability), net
Fair Value Level 3 Rollforward
Balance at the beginning of the period	(1,952.7)	[5]	(2,140.0)	[5]	(1,303.9)	[5]	(1,869.9)	[5]
Total pretax realized and unrealized gains/(losses) recorded in
Net Income (loss)	260.7	[1],[5],[6]	(64.8)	[1],[5],[6]	(430.0)	[1],[5],[6]	(301.0)	[1],[5],[6]
Other comprehensive income (loss)	0	[1],[5]	0	[1],[5]	0	[1],[5]	0	[1],[5]
Purchases	0	[5]	0	[5]	0	[5]	0	[5]
Sales							0	[5]
Settlements	26.0	[5]	17.3	[5]	67.9	[5]	(16.6)	[5]
Consolidations, Deconsolidations, net	0	[5]	0	[5]	0	[5]	0	[5]
Balance at the end of the period	(1,666.0)	[5]	(2,187.5)	[5]	(1,666.0)	[5]	(2,187.5)	[5]
Total pre-tax realized/unrealized gains/(losses) recorded in
Change in unrealized gains/(losses) related to financial instruments held at the reporting date	282.5	[5]	(28.9)	[5]	(352.1)	[5]	(311.7)	[5]
FG VIEs' liabilities with recourse, at fair value
Fair Value Level 3 Rollforward
Balance at the beginning of the period	(2,365.2)		(2,874.2)		(2,396.9)		(3,030.9)
Total pretax realized and unrealized gains/(losses) recorded in
Net Income (loss)	(17.7)	[1],[3]	14.9	[1],[3]	(135.7)	[1],[3]	3.8	[1],[3]
Other comprehensive income (loss)	0	[1]	0	[1]	0	[1]	0	[1]
Purchases	0		0		0		0
Sales			0				0
Settlements	143.9		282.8		314.2		450.6
Consolidations, Deconsolidations, net	0		(272.4)		(20.6)		(272.4)
Balance at the end of the period	(2,239.0)		(2,848.9)		(2,239.0)		(2,848.9)
Total pre-tax realized/unrealized gains/(losses) recorded in
Change in unrealized gains/(losses) related to financial instruments held at the reporting date	(17.5)		(7.1)		(124.5)		(43.0)
FG VIEs' liabilities without recourse, at fair value
Fair Value Level 3 Rollforward
Balance at the beginning of the period	(1,085.6)		(1,373.0)		(1,061.5)		(1,337.2)
Total pretax realized and unrealized gains/(losses) recorded in
Net Income (loss)	(13.5)	[1],[3]	86.5	[1],[3]	(93.3)	[1],[3]	(49.0)	[1],[3]
Other comprehensive income (loss)	0	[1]	0	[1]	0	[1]	0	[1]
Purchases	0		0		0		0
Sales							0
Settlements	56.8		67.1		112.5		166.8
Consolidations, Deconsolidations, net	0		(63.1)		0		(63.1)
Balance at the end of the period	(1,042.3)		(1,282.5)		(1,042.3)		(1,282.5)
Total pre-tax realized/unrealized gains/(losses) recorded in
Change in unrealized gains/(losses) related to financial instruments held at the reporting date	$ (37.2)		$ 52.9		$ (155.3)		$ (119.1)

[1] Realized and unrealized gains (losses) from changes in values of Level 3 financial instruments represent gains (losses) from changes in values of those financial instruments only for the periods in which the instruments were classified as Level 3.

[2] Included in net realized investment gains (losses) and net investment income.

[3] Included in fair value gains (losses) on FG VIEs.

[4] Recorded in fair value gain (loss) on committed capital securities.

[5] Represents net position of credit derivatives. The consolidated balance sheet presents gross assets and liabilities based on net counterparty exposure.

[6] Reported in net change in fair value of credit derivatives.