Investments (Details 3) (USD $) In Millions	Sep. 30, 2011	Dec. 31, 2010
Municipal Bonds
Investments
Fair Value	$ 5,002.6	$ 4,481.6
Amortized Cost	4,725.5	4,465.3
Municipal Bonds \| Texas
Investments
Fair Value	744.9	623.1
Amortized Cost	703.0	620.7
Municipal Bonds \| New York
Investments
Fair Value	661.7	547.6
Amortized Cost	627.5	545.1
Municipal Bonds \| California
Investments
Fair Value	375.3	403.4
Amortized Cost	349.9	401.0
Municipal Bonds \| Florida
Investments
Fair Value	352.6	303.9
Amortized Cost	329.8	300.5
Municipal Bonds \| Illinois
Investments
Fair Value	298.1	297.1
Amortized Cost	282.9	300.9
Municipal Bonds \| Washington
Investments
Fair Value	207.1	206.4
Amortized Cost	195.5	204.6
Municipal Bonds \| Massachusetts
Investments
Fair Value	205.5	183.9
Amortized Cost	191.2	185.8
Municipal Bonds \| Arizona
Investments
Fair Value	180.0	145.1
Amortized Cost	171.7	145.5
Municipal Bonds \| Ohio
Investments
Fair Value	138.6
Amortized Cost	131.1
Municipal Bonds \| Michigan
Investments
Fair Value	123.1	132.6
Amortized Cost	117.4	131.4
Municipal Bonds \| Georgia
Investments
Fair Value		124.8
Amortized Cost		125.4
Municipal Bonds \| All other states
Investments
Fair Value	1,715.7	1,513.7
Amortized Cost	1,625.5	1,504.4
Pre-refunded Bond
Investments
Fair Value	365.8	478.3
State General Obligation
Investments
Fair Value	665.5	519.2
State General Obligation \| Texas
Investments
Fair Value	91.7	76.8
State General Obligation \| New York
Investments
Fair Value	12.1	11.4
State General Obligation \| California
Investments
Fair Value	18.6	17.2
State General Obligation \| Florida
Investments
Fair Value	45.9	45.2
State General Obligation \| Illinois
Investments
Fair Value	23.2	10.5
State General Obligation \| Washington
Investments
Fair Value	60.2	80.0
State General Obligation \| Massachusetts
Investments
Fair Value	41.6	38.0
State General Obligation \| Ohio
Investments
Fair Value	36.2
State General Obligation \| Georgia
Investments
Fair Value		19.3
State General Obligation \| All other states
Investments
Fair Value	336.0	220.8
Local General Obligation
Investments
Fair Value	969.5	871.6
Local General Obligation \| Texas
Investments
Fair Value	335.8	294.4
Local General Obligation \| New York
Investments
Fair Value	55.1	40.0
Local General Obligation \| California
Investments
Fair Value	62.4	56.0
Local General Obligation \| Florida
Investments
Fair Value	55.4	45.1
Local General Obligation \| Illinois
Investments
Fair Value	72.1	91.0
Local General Obligation \| Washington
Investments
Fair Value	38.6	37.2
Local General Obligation \| Massachusetts
Investments
Fair Value	9.5	8.6
Local General Obligation \| Arizona
Investments
Fair Value	7.5	0.6
Local General Obligation \| Ohio
Investments
Fair Value	24.3
Local General Obligation \| Michigan
Investments
Fair Value	40.0	39.5
Local General Obligation \| Georgia
Investments
Fair Value		38.4
Local General Obligation \| All other states
Investments
Fair Value	268.8	220.8
Revenue bonds
Investments
Fair Value	3,367.6	3,090.8
Amortized Cost	3,186.8	3,085.9
Revenue bonds \| Texas
Investments
Fair Value	317.4	251.9
Revenue bonds \| New York
Investments
Fair Value	594.5	496.2
Revenue bonds \| California
Investments
Fair Value	294.3	330.2
Revenue bonds \| Florida
Investments
Fair Value	251.3	213.6
Revenue bonds \| Illinois
Investments
Fair Value	202.8	195.6
Revenue bonds \| Washington
Investments
Fair Value	108.3	89.2
Revenue bonds \| Massachusetts
Investments
Fair Value	154.4	137.3
Revenue bonds \| Arizona
Investments
Fair Value	172.5	144.5
Revenue bonds \| Ohio
Investments
Fair Value	78.1
Revenue bonds \| Michigan
Investments
Fair Value	83.1	93.1
Revenue bonds \| Georgia
Investments
Fair Value		67.1
Revenue bonds \| All other states
Investments
Fair Value	1,110.9	1,072.1
Revenue bonds \| Transportation
Investments
Fair Value	778.3	725.5
Amortized Cost	733.9	718.9
Revenue bonds \| Tax Backed
Investments
Fair Value	633.0	609.0
Amortized Cost	597.1	607.2
Revenue bonds \| Water and sewer
Investments
Fair Value	533.7	470.6
Amortized Cost	509.3	471.3
Revenue bonds \| Municipal utilities
Investments
Fair Value	510.2	457.8
Amortized Cost	480.9	456.8
Revenue bonds \| Higher Education
Investments
Fair Value	352.8	298.2
Amortized Cost	329.7	302.1
Revenue bonds \| Healthcare
Investments
Fair Value	261.5	207.3
Amortized Cost	248.5	206.5
Revenue bonds \| All other revenue sources
Investments
Fair Value	298.1	322.4
Amortized Cost	$ 287.4	$ 323.1

- Definition

This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. This item represents Available-for-sale Securities which consist of all investments in certain debt and equity securities neither classified as trading or held-to-maturity securities. A debt security represents a creditor relationship with an enterprise. Debt securities include, among other items, US Treasury securities, US government securities, municipal securities, corporate bonds, convertible debt, commercial paper, and all securitized debt instruments. An equity security represents an ownership interest in an enterprise or the right to acquire or dispose of an ownership interest in an enterprise at fixed or determinable prices. Equity securities include, among other things, common stock, certain preferred stock, warrant rights, call options, and put options, but do not include convertible debt. An entity may opt to provide the reader with additional narrative text to better understand the nature of investments in debt and equity securities which are categorized as Available-for-sale.

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