8. Investing Activities (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Available-for-sale debt securities Amortized Cost	$ 11,508.5	$ 11,267.0
Available-for-sale debt securities Gross Unrealized Gains	1,104.6	874.6
Available-for-sale debt securities Gross Unrealized Losses(1)	(176.4)	(344.6)
Available-for-sale debt securities Fair Value	12,436.7	11,797.0
Available-for-sale debt securities OTTI Recognized in AOCI(2)	(148.7)	(160.6)
Amounts applicable to the closed block debt security amortized cost	5,810.7	5,884.0
Amounts applicable to the closed block debt security Gross Unrealized Gains	665.7	565.7
Amounts applicable to the closed block debt security Gross Unrealized Gains	(52.3)	(126.2)
Amounts applicable to the closed block debt security Fair Value	6,424.1	6,323.5
Amounts applicable to the closed block debt security OTTI Recognized in AOCI(2)	(49.4)	(53.1)
Available-for-sale equity securities Amortized Cost	28.2	32.6
Available-for-sale equity securities Gross Unrealized Gains	9.4	10.9
Available-for-sale equity securities, Gross Unrealized Losses	(6.7)	(7.8)
Available-for-sale equity securities Fair Value	30.9	35.7
Available-for-sale equity securities OTTI Recognized in AOCI(2)
Amounts applicable to the closed block equity security amortized cost	11.2	13.4
Amounts applicable to the closed block equity security Gross Unrealized Gains	1.7	3.2
Amounts applicable to the closed block equity security Gross Unrealized Losses	(3.5)	(4.0)
Amounts applicable to the closed block equity security Fair Value	9.4	12.6
Amounts applicable to the closed block equity security OTTI Recognized in AOCI(2)
U.S. government and agency [Member]
Available-for-sale debt securities Amortized Cost	872.8
Available-for-sale debt securities Gross Unrealized Gains	65.3
Available-for-sale debt securities Gross Unrealized Losses(1)	(5.4)
Available-for-sale debt securities Fair Value	932.7
Available-for-sale debt securities OTTI Recognized in AOCI(2)
U.S. government and agency [Member] | As restated and amended [Member]
Available-for-sale debt securities Amortized Cost		678.0
Available-for-sale debt securities Gross Unrealized Gains		71.6
Available-for-sale debt securities Gross Unrealized Losses(1)		(7.8)
Available-for-sale debt securities Fair Value		741.8
Available-for-sale debt securities OTTI Recognized in AOCI(2)
State and political subdivision [Member]
Available-for-sale debt securities Amortized Cost	309.1
Available-for-sale debt securities Gross Unrealized Gains	38.5
Available-for-sale debt securities Gross Unrealized Losses(1)	(3.1)
Available-for-sale debt securities Fair Value	344.5
Available-for-sale debt securities OTTI Recognized in AOCI(2)
State and political subdivision [Member] | As restated and amended [Member]
Available-for-sale debt securities Amortized Cost		259.3
Available-for-sale debt securities Gross Unrealized Gains		25.4
Available-for-sale debt securities Gross Unrealized Losses(1)		(2.9)
Available-for-sale debt securities Fair Value		281.8
Available-for-sale debt securities OTTI Recognized in AOCI(2)
Foreign government [Member]
Available-for-sale debt securities Amortized Cost	180.2
Available-for-sale debt securities Gross Unrealized Gains	34.4
Available-for-sale debt securities Gross Unrealized Losses(1)
Available-for-sale debt securities Fair Value	214.6
Available-for-sale debt securities OTTI Recognized in AOCI(2)
Foreign government [Member] | As restated and amended [Member]
Available-for-sale debt securities Amortized Cost		185.7
Available-for-sale debt securities Gross Unrealized Gains		21.2
Available-for-sale debt securities Gross Unrealized Losses(1)		(1.7)
Available-for-sale debt securities Fair Value		205.2
Available-for-sale debt securities OTTI Recognized in AOCI(2)
Corporate [Member]
Available-for-sale debt securities Amortized Cost	6,736.1
Available-for-sale debt securities Gross Unrealized Gains	757.2
Available-for-sale debt securities Gross Unrealized Losses(1)	(86.9)
Available-for-sale debt securities Fair Value	7,406.4
Available-for-sale debt securities OTTI Recognized in AOCI(2)	(5.8)
Corporate [Member] | As restated and amended [Member]
Available-for-sale debt securities Amortized Cost		6,127.9
Available-for-sale debt securities Gross Unrealized Gains		601.7
Available-for-sale debt securities Gross Unrealized Losses(1)		(171.4)
Available-for-sale debt securities Fair Value		6,558.2
Available-for-sale debt securities OTTI Recognized in AOCI(2)		(5.8)
Commercial mortgage-backed (CMBS) [Member]
Available-for-sale debt securities Amortized Cost	905.9
Available-for-sale debt securities Gross Unrealized Gains	75.7
Available-for-sale debt securities Gross Unrealized Losses(1)	(8.3)
Available-for-sale debt securities Fair Value	973.3
Available-for-sale debt securities OTTI Recognized in AOCI(2)	(21.8)
Commercial mortgage-backed (CMBS) [Member] | As restated and amended [Member]
Available-for-sale debt securities Amortized Cost		1,098.9
Available-for-sale debt securities Gross Unrealized Gains		50.4
Available-for-sale debt securities Gross Unrealized Losses(1)		(20.0)
Available-for-sale debt securities Fair Value		1,129.3
Available-for-sale debt securities OTTI Recognized in AOCI(2)		(29.2)
Residential mortgage-backed (RMBS) [Member]
Available-for-sale debt securities Amortized Cost	1,808.5
Available-for-sale debt securities Gross Unrealized Gains	102.4
Available-for-sale debt securities Gross Unrealized Losses(1)	(29.3)
Available-for-sale debt securities Fair Value	1,881.6
Available-for-sale debt securities OTTI Recognized in AOCI(2)	(98.5)
Residential mortgage-backed (RMBS) [Member] | As restated and amended [Member]
Available-for-sale debt securities Amortized Cost		2,094.7
Available-for-sale debt securities Gross Unrealized Gains		82.9
Available-for-sale debt securities Gross Unrealized Losses(1)		(70.6)
Available-for-sale debt securities Fair Value		2,107.0
Available-for-sale debt securities OTTI Recognized in AOCI(2)		(92.2)
CDO/CLO [Member]
Available-for-sale debt securities Amortized Cost	242.9
Available-for-sale debt securities Gross Unrealized Gains	4.0
Available-for-sale debt securities Gross Unrealized Losses(1)	(30.4)
Available-for-sale debt securities Fair Value	216.5
Available-for-sale debt securities OTTI Recognized in AOCI(2)	(28.5)
CDO/CLO [Member] | As restated and amended [Member]
Available-for-sale debt securities Amortized Cost		283.8
Available-for-sale debt securities Gross Unrealized Gains		2.5
Available-for-sale debt securities Gross Unrealized Losses(1)		(53.9)
Available-for-sale debt securities Fair Value		232.4
Available-for-sale debt securities OTTI Recognized in AOCI(2)		(36.2)
Other asset-backed [Member]
Available-for-sale debt securities Amortized Cost	453.0
Available-for-sale debt securities Gross Unrealized Gains	27.1
Available-for-sale debt securities Gross Unrealized Losses(1)	(13.0)
Available-for-sale debt securities Fair Value	467.1
Available-for-sale debt securities OTTI Recognized in AOCI(2)	5.9
Other asset-backed [Member] | As restated and amended [Member]
Available-for-sale debt securities Amortized Cost		538.7
Available-for-sale debt securities Gross Unrealized Gains		18.9
Available-for-sale debt securities Gross Unrealized Losses(1)		(16.3)
Available-for-sale debt securities Fair Value		541.3
Available-for-sale debt securities OTTI Recognized in AOCI(2)		$ 2.8