Investment Securities (Mortgage-backed Asset Securities) (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012		Dec. 31, 2011		Sep. 30, 2011		Dec. 31, 2010
Level 2 Inputs
Investment securities
Fair value investments	$ 5,016.0		$ 6,088.2		$ 4,969.5		$ 5,477.4
Level 2 Inputs | Government National Mortgage Association Certificates and Obligations (GNMA) [Member]
Investment securities
Fair value investments	1,165.5		1,365.8
Level 2 Inputs | Federal National Mortgage Association Certificates and Obligations (FNMA) [Member]
Investment securities
Fair value investments	97.2		712.6
Level 2 Inputs | Federal Home Loan Mortgage Corporation Certificates and Obligations (FHLMC) [Member]
Investment securities
Fair value investments	37.6		35.9
Level 2 Inputs | Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Investment securities
Fair value investments	1,300.3	[1]	2,114.3	[1]
Level 2 Inputs | Residential Mortgage Backed Securities [Member]
Investment securities
Fair value investments	160.5		68.0
Level 2 Inputs | Commercial Mortgage Backed Securities [Member]
Investment securities
Fair value investments	383.8		276.7
Level 2 Inputs | Mortgage-backed Securities, Issued by Private Enterprises [Member]
Investment securities
Fair value investments	544.3		344.7
Level 2 Inputs | Collateralized Mortgage Backed Securities [Member]
Investment securities
Fair value investments	1,844.6		2,459.0
Level 2 Inputs | Collateralized Credit Card Securities [Member]
Investment securities
Fair value investments	80.8		380.6
Level 2 Inputs | Collateralized Auto Loans [Member]
Investment securities
Fair value investments	80.3		345.6
Level 2 Inputs | Collateralized Securities, Other [Member]
Investment securities
Fair value investments	36.2		22.6
Level 2 Inputs | Asset-backed Securities, Securitized Loans and Receivables [Member]
Investment securities
Fair value investments	197.3		748.8
Level 2 Inputs | Mortgage-backed and asset-backed securities
Investment securities
Fair value investments	2,041.9		3,207.8
Level 3 Inputs
Investment securities
Fair value investments							0
Level 3 Inputs | Government National Mortgage Association Certificates and Obligations (GNMA) [Member]
Investment securities
Fair value investments	0		0
Level 3 Inputs | Federal National Mortgage Association Certificates and Obligations (FNMA) [Member]
Investment securities
Fair value investments	0		0
Level 3 Inputs | Federal Home Loan Mortgage Corporation Certificates and Obligations (FHLMC) [Member]
Investment securities
Fair value investments	0		0
Level 3 Inputs | Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Investment securities
Fair value investments	0	[1]	0	[1]
Level 3 Inputs | Residential Mortgage Backed Securities [Member]
Investment securities
Fair value investments	0		15.1
Level 3 Inputs | Commercial Mortgage Backed Securities [Member]
Investment securities
Fair value investments	5.5		0
Level 3 Inputs | Mortgage-backed Securities, Issued by Private Enterprises [Member]
Investment securities
Fair value investments	5.5		15.1
Level 3 Inputs | Collateralized Mortgage Backed Securities [Member]
Investment securities
Fair value investments	5.5		15.1
Level 3 Inputs | Collateralized Credit Card Securities [Member]
Investment securities
Fair value investments	0		0
Level 3 Inputs | Collateralized Auto Loans [Member]
Investment securities
Fair value investments	0		0
Level 3 Inputs | Collateralized Securities, Other [Member]
Investment securities
Fair value investments	0		0
Level 3 Inputs | Asset-backed Securities, Securitized Loans and Receivables [Member]
Investment securities
Fair value investments	0		0
Level 3 Inputs | Mortgage-backed and asset-backed securities
Investment securities
Fair value investments	5.5		15.1
Fair Value
Investment securities
Fair value investments	7,626.4	[2]	8,346.8	[2],[3]	7,265.9	[2]	7,901.6	[2]
Fair Value | Government National Mortgage Association Certificates and Obligations (GNMA) [Member]
Investment securities
Fair value investments	1,165.5		1,365.8
Fair Value | Federal National Mortgage Association Certificates and Obligations (FNMA) [Member]
Investment securities
Fair value investments	97.2		712.6
Fair Value | Federal Home Loan Mortgage Corporation Certificates and Obligations (FHLMC) [Member]
Investment securities
Fair value investments	37.6		35.9
Fair Value | Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Investment securities
Fair value investments	1,300.3	[1]	2,114.3	[1]
Fair Value | Residential Mortgage Backed Securities [Member]
Investment securities
Fair value investments	160.5		83.1
Fair Value | Commercial Mortgage Backed Securities [Member]
Investment securities
Fair value investments	389.3		276.7
Fair Value | Mortgage-backed Securities, Issued by Private Enterprises [Member]
Investment securities
Fair value investments	549.8		359.8
Fair Value | Collateralized Mortgage Backed Securities [Member]
Investment securities
Fair value investments	1,850.1		2,474.1
Fair Value | Collateralized Credit Card Securities [Member]
Investment securities
Fair value investments	80.8		380.6
Fair Value | Collateralized Auto Loans [Member]
Investment securities
Fair value investments	80.3		345.6
Fair Value | Collateralized Securities, Other [Member]
Investment securities
Fair value investments	36.2		22.6
Fair Value | Asset-backed Securities, Securitized Loans and Receivables [Member]
Investment securities
Fair value investments	197.3		748.8
Fair Value | Mortgage-backed and asset-backed securities
Investment securities
Fair value investments	$ 2,047.4		$ 3,222.9

[1] (1) Represents publicly traded mortgage-backed securities which carry the full faith and credit guaranty of the U.S. government (i.e., GNMA) or are guaranteed by a government sponsored entity (i.e., FNMA, FHLMC).

[2] (1) Excludes carrying value of $33.0 and $34.3 at January 1, 2012 and September 30, 2012 associated with other long-term investments accounted for using the equity method

[3] (2) Carrying value includes $111.8 and $377.3 at January 1, 2012 and September 30, 2012 that is classified as assets held for sale relating to discontinued operations. Level 3 Investments MillionsLevel 1InvestmentsLevel 2InvestmentsFixedMaturitiesCommonequitysecuritiesConvertiblefixedmaturitiesOther long-terminvestments Total Balance at January 1, 2011$1,894.4$5,477.4$128.4$71.2$—$330.2(1) $7,901.6(1) Total realized and unrealized gains (losses)(50.5)115.9(10.6)(4.9)—22.5 72.4 Foreign currency gains (losses) through OCI.3(84.4)(4.4)1.6—(5.0) (91.9) Amortization/Accretion2.4(40.7)(.1)——— (38.4) Purchases6,690.73,987.4212.819.7—27.9 10,938.5 Sales(6,782.1)(4,596.9)1.6(55.5)—(83.4) (11,516.3) Transfers in—111.81.0——— 112.8 Transfers out—(1.0)(111.8)——— (112.8) Balance at September 30, 2011$1,755.2$4,969.5$216.9$32.1$—$292.2(1) $7,265.9(1) (1) Excludes carrying value o