Investment Securities (Fair Value Measurement by Level) (Details) - USD ($)
$ in Millions

Sep. 30, 2015

Dec. 31, 2014

Sep. 30, 2014

Dec. 31, 2013

Schedule of Trading Securities and Other Trading Assets [Line Items]

Fair value investments

$ 3,365.4

$ 3,343.6

$ 3,610.7

$ 3,889.0

Other Investments

294.6

318.0

Short-term investments, at amortized cost (which approximates fair value)

325.0

376.8

Level 1 Inputs

Schedule of Trading Securities and Other Trading Assets [Line Items]

Fair value investments

418.2

550.6

766.2

997.2

Level 2 Inputs

Schedule of Trading Securities and Other Trading Assets [Line Items]

Fair value investments

2,561.6

2,372.9

2,495.9

2,575.4

Debt securities issued by corporations

Schedule of Trading Securities and Other Trading Assets [Line Items]

Fair value investments

1,005.8

1,171.7

Mortgage-backed and asset-backed securities

Schedule of Trading Securities and Other Trading Assets [Line Items]

Fair value investments

1,265.4

967.9

Mortgage-backed and asset-backed securities | Level 2 Inputs

Schedule of Trading Securities and Other Trading Assets [Line Items]

Fair value investments

1,265.4

967.9

Mortgage-backed and asset-backed securities | Level 3 Inputs

Schedule of Trading Securities and Other Trading Assets [Line Items]

Fair value investments

0.0

Fixed maturity investments. | Level 3 Inputs

Schedule of Trading Securities and Other Trading Assets [Line Items]

Fair value investments

70.3

76.4

88.0

81.8

Common equity securities | Level 3 Inputs

Schedule of Trading Securities and Other Trading Assets [Line Items]

Fair value investments

34.2

39.5

38.2

45.4

Convertible fixed maturity investments | Level 3 Inputs

Schedule of Trading Securities and Other Trading Assets [Line Items]

Fair value investments

5.6

8.2

10.9

6.1

Other long-term investments | Level 3 Inputs

Schedule of Trading Securities and Other Trading Assets [Line Items]

Fair value investments

275.5

296.0

211.5

183.1

Fair value measured on a recurring basis

Schedule of Trading Securities and Other Trading Assets [Line Items]

Fair value investments

3,690.4

3,720.4

Fair value measured on a recurring basis | Level 1 Inputs

Schedule of Trading Securities and Other Trading Assets [Line Items]

Fair value investments

743.2

926.9

Fair value measured on a recurring basis | Level 2 Inputs

Schedule of Trading Securities and Other Trading Assets [Line Items]

Fair value investments

2,561.6

2,373.4

Fair value measured on a recurring basis | Level 3 Inputs

Schedule of Trading Securities and Other Trading Assets [Line Items]

Fair value investments

385.6

420.1

Fair value measured on a recurring basis | U.S. Government and agency obligations

Schedule of Trading Securities and Other Trading Assets [Line Items]

Fair value investments

99.8

105.2

Fair value measured on a recurring basis | U.S. Government and agency obligations | Level 1 Inputs

Schedule of Trading Securities and Other Trading Assets [Line Items]

Fair value investments

61.8

51.2

Fair value measured on a recurring basis | U.S. Government and agency obligations | Level 2 Inputs

Schedule of Trading Securities and Other Trading Assets [Line Items]

Fair value investments

38.0

54.0

Fair value measured on a recurring basis | U.S. Government and agency obligations | Level 3 Inputs

Schedule of Trading Securities and Other Trading Assets [Line Items]

Fair value investments

0.0

Fair value measured on a recurring basis | Debt securities issued by corporations

Schedule of Trading Securities and Other Trading Assets [Line Items]

Fair value investments

1,005.8

1,171.7

Fair value measured on a recurring basis | Debt securities issued by corporations | Level 1 Inputs

Schedule of Trading Securities and Other Trading Assets [Line Items]

Fair value investments

0.0

Fair value measured on a recurring basis | Debt securities issued by corporations | Level 2 Inputs

Schedule of Trading Securities and Other Trading Assets [Line Items]

Fair value investments

1,005.8

1,166.4

Fair value measured on a recurring basis | Debt securities issued by corporations | Level 3 Inputs

Schedule of Trading Securities and Other Trading Assets [Line Items]

Fair value investments

0.0

5.3

Fair value measured on a recurring basis | Debt securities issued by corporations | Consumer

Schedule of Trading Securities and Other Trading Assets [Line Items]

Fair value investments

223.1

259.2

Fair value measured on a recurring basis | Debt securities issued by corporations | Consumer | Level 1 Inputs

Schedule of Trading Securities and Other Trading Assets [Line Items]

Fair value investments

0.0

Fair value measured on a recurring basis | Debt securities issued by corporations | Consumer | Level 2 Inputs

Schedule of Trading Securities and Other Trading Assets [Line Items]

Fair value investments

223.1

259.2

Fair value measured on a recurring basis | Debt securities issued by corporations | Consumer | Level 3 Inputs

Schedule of Trading Securities and Other Trading Assets [Line Items]

Fair value investments

0.0

Fair value measured on a recurring basis | Debt securities issued by corporations | Industrial

Schedule of Trading Securities and Other Trading Assets [Line Items]

Fair value investments

132.8

107.3

Fair value measured on a recurring basis | Debt securities issued by corporations | Industrial | Level 1 Inputs

Schedule of Trading Securities and Other Trading Assets [Line Items]

Fair value investments

0.0

Fair value measured on a recurring basis | Debt securities issued by corporations | Industrial | Level 2 Inputs

Schedule of Trading Securities and Other Trading Assets [Line Items]

Fair value investments

132.8

102.0

Fair value measured on a recurring basis | Debt securities issued by corporations | Industrial | Level 3 Inputs

Schedule of Trading Securities and Other Trading Assets [Line Items]

Fair value investments

0.0

5.3

Fair value measured on a recurring basis | Debt securities issued by corporations | Financials

Schedule of Trading Securities and Other Trading Assets [Line Items]

Fair value investments

201.3

254.7

Fair value measured on a recurring basis | Debt securities issued by corporations | Financials | Level 1 Inputs

Schedule of Trading Securities and Other Trading Assets [Line Items]

Fair value investments

0.0

Fair value measured on a recurring basis | Debt securities issued by corporations | Financials | Level 2 Inputs

Schedule of Trading Securities and Other Trading Assets [Line Items]

Fair value investments

201.3

254.7

Fair value measured on a recurring basis | Debt securities issued by corporations | Financials | Level 3 Inputs

Schedule of Trading Securities and Other Trading Assets [Line Items]

Fair value investments

0.0

Fair value measured on a recurring basis | Debt securities issued by corporations | Communications [Member]

Schedule of Trading Securities and Other Trading Assets [Line Items]

Fair value investments

52.7

71.5

Fair value measured on a recurring basis | Debt securities issued by corporations | Communications [Member] | Level 1 Inputs

Schedule of Trading Securities and Other Trading Assets [Line Items]

Fair value investments

0.0

Fair value measured on a recurring basis | Debt securities issued by corporations | Communications [Member] | Level 2 Inputs

Schedule of Trading Securities and Other Trading Assets [Line Items]

Fair value investments

52.7

71.5

Fair value measured on a recurring basis | Debt securities issued by corporations | Communications [Member] | Level 3 Inputs

Schedule of Trading Securities and Other Trading Assets [Line Items]

Fair value investments

0.0

Fair value measured on a recurring basis | Debt securities issued by corporations | Health Care [Member]

Schedule of Trading Securities and Other Trading Assets [Line Items]

Fair value investments

177.2

181.8

Fair value measured on a recurring basis | Debt securities issued by corporations | Health Care [Member] | Level 1 Inputs

Schedule of Trading Securities and Other Trading Assets [Line Items]

Fair value investments

0.0

Fair value measured on a recurring basis | Debt securities issued by corporations | Health Care [Member] | Level 2 Inputs

Schedule of Trading Securities and Other Trading Assets [Line Items]

Fair value investments

177.2

181.8

Fair value measured on a recurring basis | Debt securities issued by corporations | Health Care [Member] | Level 3 Inputs

Schedule of Trading Securities and Other Trading Assets [Line Items]

Fair value investments

0.0

Fair value measured on a recurring basis | Debt securities issued by corporations | Energy

Schedule of Trading Securities and Other Trading Assets [Line Items]

Fair value investments

57.8

65.6

Fair value measured on a recurring basis | Debt securities issued by corporations | Energy | Level 1 Inputs

Schedule of Trading Securities and Other Trading Assets [Line Items]

Fair value investments

0.0

Fair value measured on a recurring basis | Debt securities issued by corporations | Energy | Level 2 Inputs

Schedule of Trading Securities and Other Trading Assets [Line Items]

Fair value investments

57.8

65.6

Fair value measured on a recurring basis | Debt securities issued by corporations | Energy | Level 3 Inputs

Schedule of Trading Securities and Other Trading Assets [Line Items]

Fair value investments

0.0

Fair value measured on a recurring basis | Debt securities issued by corporations | Technology

Schedule of Trading Securities and Other Trading Assets [Line Items]

Fair value investments

64.7

88.3

Fair value measured on a recurring basis | Debt securities issued by corporations | Technology | Level 1 Inputs

Schedule of Trading Securities and Other Trading Assets [Line Items]

Fair value investments

0.0

Fair value measured on a recurring basis | Debt securities issued by corporations | Technology | Level 2 Inputs

Schedule of Trading Securities and Other Trading Assets [Line Items]

Fair value investments

64.7

88.3

Fair value measured on a recurring basis | Debt securities issued by corporations | Technology | Level 3 Inputs

Schedule of Trading Securities and Other Trading Assets [Line Items]

Fair value investments

0.0

Fair value measured on a recurring basis | Debt securities issued by corporations | Utilities

Schedule of Trading Securities and Other Trading Assets [Line Items]

Fair value investments

62.5

84.1

Fair value measured on a recurring basis | Debt securities issued by corporations | Utilities | Level 1 Inputs

Schedule of Trading Securities and Other Trading Assets [Line Items]

Fair value investments

0.0

Fair value measured on a recurring basis | Debt securities issued by corporations | Utilities | Level 2 Inputs

Schedule of Trading Securities and Other Trading Assets [Line Items]

Fair value investments

62.5

84.1

Fair value measured on a recurring basis | Debt securities issued by corporations | Utilities | Level 3 Inputs

Schedule of Trading Securities and Other Trading Assets [Line Items]

Fair value investments

0.0

Fair value measured on a recurring basis | Debt securities issued by corporations | Materials

Schedule of Trading Securities and Other Trading Assets [Line Items]

Fair value investments

31.4

51.7

Fair value measured on a recurring basis | Debt securities issued by corporations | Materials | Level 1 Inputs

Schedule of Trading Securities and Other Trading Assets [Line Items]

Fair value investments

0.0

Fair value measured on a recurring basis | Debt securities issued by corporations | Materials | Level 2 Inputs

Schedule of Trading Securities and Other Trading Assets [Line Items]

Fair value investments

31.4

51.7

Fair value measured on a recurring basis | Debt securities issued by corporations | Materials | Level 3 Inputs

Schedule of Trading Securities and Other Trading Assets [Line Items]

Fair value investments

0.0

Fair value measured on a recurring basis | Debt securities issued by corporations | Other:

Schedule of Trading Securities and Other Trading Assets [Line Items]

Fair value investments

2.3

7.5

Fair value measured on a recurring basis | Debt securities issued by corporations | Other: | Level 1 Inputs

Schedule of Trading Securities and Other Trading Assets [Line Items]

Fair value investments

0.0

Fair value measured on a recurring basis | Debt securities issued by corporations | Other: | Level 2 Inputs

Schedule of Trading Securities and Other Trading Assets [Line Items]

Fair value investments

2.3

7.5

Fair value measured on a recurring basis | Debt securities issued by corporations | Other: | Level 3 Inputs

Schedule of Trading Securities and Other Trading Assets [Line Items]

Fair value investments

0.0

Fair value measured on a recurring basis | Municipal obligations

Schedule of Trading Securities and Other Trading Assets [Line Items]

Fair value investments

146.8

967.9

Fair value measured on a recurring basis | Municipal obligations | Level 1 Inputs

Schedule of Trading Securities and Other Trading Assets [Line Items]

Fair value investments

0.0

Fair value measured on a recurring basis | Municipal obligations | Level 2 Inputs

Schedule of Trading Securities and Other Trading Assets [Line Items]

Fair value investments

146.8

967.9

Fair value measured on a recurring basis | Municipal obligations | Level 3 Inputs

Schedule of Trading Securities and Other Trading Assets [Line Items]

Fair value investments

0.0

Fair value measured on a recurring basis | Mortgage-backed and asset-backed securities

Schedule of Trading Securities and Other Trading Assets [Line Items]

Fair value investments

1,265.4

10.8

Fair value measured on a recurring basis | Mortgage-backed and asset-backed securities | Level 1 Inputs

Schedule of Trading Securities and Other Trading Assets [Line Items]

Fair value investments

0.0

0.6

Fair value measured on a recurring basis | Mortgage-backed and asset-backed securities | Level 2 Inputs

Schedule of Trading Securities and Other Trading Assets [Line Items]

Fair value investments

1,265.4

10.2

Fair value measured on a recurring basis | Mortgage-backed and asset-backed securities | Level 3 Inputs

Schedule of Trading Securities and Other Trading Assets [Line Items]

Fair value investments

0.0

Fair value measured on a recurring basis | Foreign government, agency and provincial obligations

Schedule of Trading Securities and Other Trading Assets [Line Items]

Fair value investments

1.3

84.2

Fair value measured on a recurring basis | Foreign government, agency and provincial obligations | Level 1 Inputs

Schedule of Trading Securities and Other Trading Assets [Line Items]

Fair value investments

0.6

0.0

Fair value measured on a recurring basis | Foreign government, agency and provincial obligations | Level 2 Inputs

Schedule of Trading Securities and Other Trading Assets [Line Items]

Fair value investments

0.7

13.1

Fair value measured on a recurring basis | Foreign government, agency and provincial obligations | Level 3 Inputs

Schedule of Trading Securities and Other Trading Assets [Line Items]

Fair value investments

0.0

71.1

Fair value measured on a recurring basis | Preferred Stock

Schedule of Trading Securities and Other Trading Assets [Line Items]

Fair value investments

83.1

82.2

Fair value measured on a recurring basis | Preferred Stock | Level 1 Inputs

Schedule of Trading Securities and Other Trading Assets [Line Items]

Fair value investments

0.0

Fair value measured on a recurring basis | Preferred Stock | Level 2 Inputs

Schedule of Trading Securities and Other Trading Assets [Line Items]

Fair value investments

12.8

82.2

Fair value measured on a recurring basis | Preferred Stock | Level 3 Inputs

Schedule of Trading Securities and Other Trading Assets [Line Items]

Fair value investments

70.3

0.0

Fair value measured on a recurring basis | Fixed maturity investments.

Schedule of Trading Securities and Other Trading Assets [Line Items]

Fair value investments

2,602.2

2,422.0

Fair value measured on a recurring basis | Fixed maturity investments. | Level 1 Inputs

Schedule of Trading Securities and Other Trading Assets [Line Items]

Fair value investments

62.4

51.8

Fair value measured on a recurring basis | Fixed maturity investments. | Level 2 Inputs

Schedule of Trading Securities and Other Trading Assets [Line Items]

Fair value investments

2,469.5

2,293.8

Fair value measured on a recurring basis | Fixed maturity investments. | Level 3 Inputs

Schedule of Trading Securities and Other Trading Assets [Line Items]

Fair value investments

70.3

76.4

Fair value measured on a recurring basis | Short-term investments

Schedule of Trading Securities and Other Trading Assets [Line Items]

Fair value investments

325.0

376.8

Fair value measured on a recurring basis | Short-term investments | Level 1 Inputs

Schedule of Trading Securities and Other Trading Assets [Line Items]

Fair value investments

325.0

376.3

Short-term investments, at amortized cost (which approximates fair value)

325.0

376.8

402.7

310.4

Fair value measured on a recurring basis | Short-term investments | Level 2 Inputs

Schedule of Trading Securities and Other Trading Assets [Line Items]

Fair value investments

0.0

0.5

Fair value measured on a recurring basis | Short-term investments | Level 3 Inputs

Schedule of Trading Securities and Other Trading Assets [Line Items]

Fair value investments

0.0

Fair value measured on a recurring basis | Common equity securities | Consumer

Schedule of Trading Securities and Other Trading Assets [Line Items]

Fair value investments

56.5

116.0

Fair value measured on a recurring basis | Common equity securities | Consumer | Level 1 Inputs

Schedule of Trading Securities and Other Trading Assets [Line Items]

Fair value investments

56.5

115.9

Fair value measured on a recurring basis | Common equity securities | Consumer | Level 2 Inputs

Schedule of Trading Securities and Other Trading Assets [Line Items]

Fair value investments

0.0

0.1

Fair value measured on a recurring basis | Common equity securities | Consumer | Level 3 Inputs

Schedule of Trading Securities and Other Trading Assets [Line Items]

Fair value investments

0.0

Fair value measured on a recurring basis | Common equity securities | Industrial

Schedule of Trading Securities and Other Trading Assets [Line Items]

Fair value investments

25.2

57.1

Fair value measured on a recurring basis | Common equity securities | Industrial | Level 1 Inputs

Schedule of Trading Securities and Other Trading Assets [Line Items]

Fair value investments

25.2

57.1

Fair value measured on a recurring basis | Common equity securities | Industrial | Level 2 Inputs

Schedule of Trading Securities and Other Trading Assets [Line Items]

Fair value investments

0.0

Fair value measured on a recurring basis | Common equity securities | Industrial | Level 3 Inputs

Schedule of Trading Securities and Other Trading Assets [Line Items]

Fair value investments

0.0

Fair value measured on a recurring basis | Common equity securities | Financials

Schedule of Trading Securities and Other Trading Assets [Line Items]

Fair value investments

63.2

180.7

Fair value measured on a recurring basis | Common equity securities | Financials | Level 1 Inputs

Schedule of Trading Securities and Other Trading Assets [Line Items]

Fair value investments

29.0

141.2

Fair value measured on a recurring basis | Common equity securities | Financials | Level 2 Inputs

Schedule of Trading Securities and Other Trading Assets [Line Items]

Fair value investments

0.0

Fair value measured on a recurring basis | Common equity securities | Financials | Level 3 Inputs

Schedule of Trading Securities and Other Trading Assets [Line Items]

Fair value investments

34.2

39.5

Fair value measured on a recurring basis | Common equity securities | Communications [Member]

Schedule of Trading Securities and Other Trading Assets [Line Items]

Fair value investments

36.0

28.5

Fair value measured on a recurring basis | Common equity securities | Communications [Member] | Level 1 Inputs

Schedule of Trading Securities and Other Trading Assets [Line Items]

Fair value investments

36.0

28.5

Fair value measured on a recurring basis | Common equity securities | Communications [Member] | Level 2 Inputs

Schedule of Trading Securities and Other Trading Assets [Line Items]

Fair value investments

0.0

Fair value measured on a recurring basis | Common equity securities | Communications [Member] | Level 3 Inputs

Schedule of Trading Securities and Other Trading Assets [Line Items]

Fair value investments

0.0

Fair value measured on a recurring basis | Common equity securities | Health Care [Member]

Schedule of Trading Securities and Other Trading Assets [Line Items]

Fair value investments

34.5

74.4

Fair value measured on a recurring basis | Common equity securities | Health Care [Member] | Level 1 Inputs

Schedule of Trading Securities and Other Trading Assets [Line Items]

Fair value investments

34.5

74.4

Fair value measured on a recurring basis | Common equity securities | Health Care [Member] | Level 2 Inputs

Schedule of Trading Securities and Other Trading Assets [Line Items]

Fair value investments

0.0

Fair value measured on a recurring basis | Common equity securities | Health Care [Member] | Level 3 Inputs

Schedule of Trading Securities and Other Trading Assets [Line Items]

Fair value investments

0.0

Fair value measured on a recurring basis | Common equity securities | Energy

Schedule of Trading Securities and Other Trading Assets [Line Items]

Fair value investments

0.0

18.1

Fair value measured on a recurring basis | Common equity securities | Energy | Level 1 Inputs

Schedule of Trading Securities and Other Trading Assets [Line Items]

Fair value investments

0.0

18.1

Fair value measured on a recurring basis | Common equity securities | Energy | Level 2 Inputs

Schedule of Trading Securities and Other Trading Assets [Line Items]

Fair value investments

0.0

Fair value measured on a recurring basis | Common equity securities | Energy | Level 3 Inputs

Schedule of Trading Securities and Other Trading Assets [Line Items]

Fair value investments

0.0

Fair value measured on a recurring basis | Common equity securities | Technology

Schedule of Trading Securities and Other Trading Assets [Line Items]

Fair value investments

22.0

44.8

Fair value measured on a recurring basis | Common equity securities | Technology | Level 1 Inputs

Schedule of Trading Securities and Other Trading Assets [Line Items]

Fair value investments

22.0

44.8

Fair value measured on a recurring basis | Common equity securities | Technology | Level 2 Inputs

Schedule of Trading Securities and Other Trading Assets [Line Items]

Fair value investments

0.0

Fair value measured on a recurring basis | Common equity securities | Technology | Level 3 Inputs

Schedule of Trading Securities and Other Trading Assets [Line Items]

Fair value investments

0.0

Fair value measured on a recurring basis | Common equity securities | Utilities

Schedule of Trading Securities and Other Trading Assets [Line Items]

Fair value investments

0.0

4.9

Fair value measured on a recurring basis | Common equity securities | Utilities | Level 1 Inputs

Schedule of Trading Securities and Other Trading Assets [Line Items]

Fair value investments

0.0

4.9

Fair value measured on a recurring basis | Common equity securities | Utilities | Level 2 Inputs

Schedule of Trading Securities and Other Trading Assets [Line Items]

Fair value investments

0.0

Fair value measured on a recurring basis | Common equity securities | Utilities | Level 3 Inputs

Schedule of Trading Securities and Other Trading Assets [Line Items]

Fair value investments

0.0

Fair value measured on a recurring basis | Common equity securities | Materials

Schedule of Trading Securities and Other Trading Assets [Line Items]

Fair value investments

0.0

12.0

Fair value measured on a recurring basis | Common equity securities | Materials | Level 1 Inputs

Schedule of Trading Securities and Other Trading Assets [Line Items]

Fair value investments

0.0

12.0

Fair value measured on a recurring basis | Common equity securities | Materials | Level 2 Inputs

Schedule of Trading Securities and Other Trading Assets [Line Items]

Fair value investments

0.0

Fair value measured on a recurring basis | Common equity securities | Materials | Level 3 Inputs

Schedule of Trading Securities and Other Trading Assets [Line Items]

Fair value investments

0.0

Fair value measured on a recurring basis | Common equity securities | Other:

Schedule of Trading Securities and Other Trading Assets [Line Items]

Fair value investments

72.1

75.2

Fair value measured on a recurring basis | Common equity securities | Other: | Level 1 Inputs

Schedule of Trading Securities and Other Trading Assets [Line Items]

Fair value investments

0.0

1.9

Fair value measured on a recurring basis | Common equity securities | Other: | Level 2 Inputs

Schedule of Trading Securities and Other Trading Assets [Line Items]

Fair value investments

72.1

73.3

Fair value measured on a recurring basis | Common equity securities | Other: | Level 3 Inputs

Schedule of Trading Securities and Other Trading Assets [Line Items]

Fair value investments

0.0

Fair value measured on a recurring basis | Common equity securities | Exchange Traded Funds [Member]

Schedule of Trading Securities and Other Trading Assets [Line Items]

Fair value investments

172.6

Fair value measured on a recurring basis | Common equity securities | Exchange Traded Funds [Member] | Level 1 Inputs

Schedule of Trading Securities and Other Trading Assets [Line Items]

Fair value investments

152.6

Fair value measured on a recurring basis | Common equity securities | Exchange Traded Funds [Member] | Level 2 Inputs

Schedule of Trading Securities and Other Trading Assets [Line Items]

Fair value investments

20.0

Fair value measured on a recurring basis | Common equity securities | Exchange Traded Funds [Member] | Level 3 Inputs

Schedule of Trading Securities and Other Trading Assets [Line Items]

Fair value investments

0.0

Fair value measured on a recurring basis | Common equity securities | Common equity securities

Schedule of Trading Securities and Other Trading Assets [Line Items]

Fair value investments

482.1

611.7

Fair value measured on a recurring basis | Common equity securities | Common equity securities | Level 1 Inputs

Schedule of Trading Securities and Other Trading Assets [Line Items]

Fair value investments

355.8

498.8

Fair value measured on a recurring basis | Common equity securities | Common equity securities | Level 2 Inputs

Schedule of Trading Securities and Other Trading Assets [Line Items]

Fair value investments

92.1

73.4

Fair value measured on a recurring basis | Common equity securities | Common equity securities | Level 3 Inputs

Schedule of Trading Securities and Other Trading Assets [Line Items]

Fair value investments

34.2

39.5

Fair value measured on a recurring basis | Convertible fixed maturity investments

Schedule of Trading Securities and Other Trading Assets [Line Items]

Fair value investments

5.6

13.9

Fair value measured on a recurring basis | Convertible fixed maturity investments | Level 1 Inputs

Schedule of Trading Securities and Other Trading Assets [Line Items]

Fair value investments

0.0

Fair value measured on a recurring basis | Convertible fixed maturity investments | Level 2 Inputs

Schedule of Trading Securities and Other Trading Assets [Line Items]

Fair value investments

0.0

5.7

Fair value measured on a recurring basis | Convertible fixed maturity investments | Level 3 Inputs

Schedule of Trading Securities and Other Trading Assets [Line Items]

Fair value investments

5.6

8.2

Fair value measured on a recurring basis | Other long-term investments

Schedule of Trading Securities and Other Trading Assets [Line Items]

Fair value investments

275.5

296.0

Carrying value of investment accounted for using the equity method

3.9

Fair value measured on a recurring basis | Other long-term investments | Level 1 Inputs

Schedule of Trading Securities and Other Trading Assets [Line Items]

Fair value investments

0.0

Fair value measured on a recurring basis | Other long-term investments | Level 2 Inputs

Schedule of Trading Securities and Other Trading Assets [Line Items]

Fair value investments

0.0

Fair value measured on a recurring basis | Other long-term investments | Level 3 Inputs

Schedule of Trading Securities and Other Trading Assets [Line Items]

Fair value investments

275.5

296.0

Carrying value of investment accounted for using the equity method

5.2

5.1

6.8

Discontinued Operations [Member]

Schedule of Trading Securities and Other Trading Assets [Line Items]

Fixed maturity investments reclassified to assets held for sale

203.9

236.3

Affordable Housing Development Fund [Member]

Schedule of Trading Securities and Other Trading Assets [Line Items]

Other Investments

15.2

16.8

$ 17.3

$ 19.1

Affordable Housing Development Fund [Member] | Fair value measured on a recurring basis | Other long-term investments

Schedule of Trading Securities and Other Trading Assets [Line Items]

Other Investments

$ 15.2

$ 16.8