Fair Value Measurements - Fair Value Inputs (Details) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value Option Investments, Fair Value Disclosure	$ 0.0	$ 77.5
Trading Securities, Fair Value Disclosure	0.0	6.7
Fair Value, Inputs, Level 3 [Member] | Partnership Interest [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Unfunded Commitments	143.2
Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading Securities, Fair Value Disclosure		6.7
Cash Flow Hedge Derivative Instrument Assets at Fair Value		(0.8)
Investments, Fair Value Disclosure	5,775.2	5,992.1
Fair Value, Measurements, Recurring [Member] | Investments in Fixed Maturities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities, Fair Value Disclosure	5,260.3	5,382.7
Fair Value, Measurements, Recurring [Member] | U.S. Government and Government Agencies and Authorities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities, Fair Value Disclosure	649.4	556.1
Fair Value, Measurements, Recurring [Member] | States and Political Subdivisions [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities, Fair Value Disclosure	1,532.4	1,701.8
Fair Value, Measurements, Recurring [Member] | Foreign Governments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities, Fair Value Disclosure	4.3	3.2
Fair Value, Measurements, Recurring [Member] | Corporate Bonds and Notes [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities, Fair Value Disclosure	2,839.4	2,980.6
Fair Value, Measurements, Recurring [Member] | Redeemable Preferred Stocks
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities, Fair Value Disclosure		0.1
Fair Value, Measurements, Recurring [Member] | Collateralized Loan Obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities, Fair Value Disclosure	229.2	139.8
Fair Value, Measurements, Recurring [Member] | Other Mortgage- and Asset-backed
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities, Fair Value Disclosure	5.6	1.1
Fair Value, Measurements, Recurring [Member] | Equity Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities, Fair Value Disclosure	514.9	526.0
Fair Value, Measurements, Recurring [Member] | Exchange Traded Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities, Fair Value Disclosure	214.6	219.5
Fair Value, Measurements, Recurring [Member] | Partnership Interest [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities, Fair Value Disclosure	229.1	202.9
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading Securities, Fair Value Disclosure		6.7
Cash Flow Hedge Derivative Instrument Assets at Fair Value		0.0
Investments, Fair Value Disclosure	337.4	349.7
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Investments in Fixed Maturities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities, Fair Value Disclosure	108.7	115.8
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | U.S. Government and Government Agencies and Authorities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities, Fair Value Disclosure	108.7	115.8
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | States and Political Subdivisions [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities, Fair Value Disclosure	0.0	0.0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Foreign Governments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities, Fair Value Disclosure	0.0	0.0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Corporate Bonds and Notes [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities, Fair Value Disclosure	0.0	0.0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Redeemable Preferred Stocks
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities, Fair Value Disclosure		0.0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Collateralized Loan Obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities, Fair Value Disclosure	0.0	0.0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Other Mortgage- and Asset-backed
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities, Fair Value Disclosure	0.0	0.0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Equity Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities, Fair Value Disclosure	228.7	227.2
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Exchange Traded Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities, Fair Value Disclosure	214.6	219.5
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Partnership Interest [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities, Fair Value Disclosure	0.0	0.0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading Securities, Fair Value Disclosure		0.0
Cash Flow Hedge Derivative Instrument Assets at Fair Value		(0.8)
Investments, Fair Value Disclosure	4,727.3	4,839.8
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Investments in Fixed Maturities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities, Fair Value Disclosure	4,670.2	4,772.1
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | U.S. Government and Government Agencies and Authorities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities, Fair Value Disclosure	540.7	440.3
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | States and Political Subdivisions [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities, Fair Value Disclosure	1,532.4	1,701.8
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Foreign Governments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities, Fair Value Disclosure	4.3	3.2
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Corporate Bonds and Notes [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities, Fair Value Disclosure	2,453.9	2,579.1
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Redeemable Preferred Stocks
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities, Fair Value Disclosure		0.0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Collateralized Loan Obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities, Fair Value Disclosure	133.3	46.6
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Other Mortgage- and Asset-backed
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities, Fair Value Disclosure	5.6	1.1
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Equity Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities, Fair Value Disclosure	57.1	68.5
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Exchange Traded Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities, Fair Value Disclosure	0.0	0.0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Partnership Interest [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities, Fair Value Disclosure	0.0	0.0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading Securities, Fair Value Disclosure		0.0
Cash Flow Hedge Derivative Instrument Assets at Fair Value		0.0
Investments, Fair Value Disclosure	481.4	556.6
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Investments in Fixed Maturities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities, Fair Value Disclosure	481.4	494.8
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | U.S. Government and Government Agencies and Authorities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities, Fair Value Disclosure	0.0	0.0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | States and Political Subdivisions [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities, Fair Value Disclosure	0.0	0.0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Foreign Governments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities, Fair Value Disclosure	0.0	0.0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Corporate Bonds and Notes [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities, Fair Value Disclosure	385.5	401.5
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Redeemable Preferred Stocks
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities, Fair Value Disclosure		0.1
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Collateralized Loan Obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities, Fair Value Disclosure	95.9	93.2
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Other Mortgage- and Asset-backed
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities, Fair Value Disclosure	0.0	0.0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Equity Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities, Fair Value Disclosure	0.0	61.8
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Exchange Traded Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities, Fair Value Disclosure	0.0	0.0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Partnership Interest [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities, Fair Value Disclosure	0.0	34.4
Finance, Insurance and Real Estate [Member] | Fair Value, Measurements, Recurring [Member] | Preferred Stock [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities, Fair Value Disclosure	44.7	55.7
Finance, Insurance and Real Estate [Member] | Fair Value, Measurements, Recurring [Member] | Common Stocks [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities, Fair Value Disclosure	1.9	7.1
Finance, Insurance and Real Estate [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Preferred Stock [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities, Fair Value Disclosure	0.0	0.0
Finance, Insurance and Real Estate [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Common Stocks [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities, Fair Value Disclosure	1.9	7.0
Finance, Insurance and Real Estate [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Preferred Stock [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities, Fair Value Disclosure	44.7	55.7
Finance, Insurance and Real Estate [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Common Stocks [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities, Fair Value Disclosure	0.0	0.1
Finance, Insurance and Real Estate [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Preferred Stock [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities, Fair Value Disclosure	0.0	0.0
Finance, Insurance and Real Estate [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Common Stocks [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities, Fair Value Disclosure	0.0	0.0
All Industries Other than Finance, Insurance and Real Estate [Member] | Fair Value, Measurements, Recurring [Member] | Preferred Stock [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities, Fair Value Disclosure	11.8	23.1
All Industries Other than Finance, Insurance and Real Estate [Member] | Fair Value, Measurements, Recurring [Member] | Common Stocks [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities, Fair Value Disclosure	12.8	17.7
All Industries Other than Finance, Insurance and Real Estate [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Preferred Stock [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities, Fair Value Disclosure	0.0	0.0
All Industries Other than Finance, Insurance and Real Estate [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Common Stocks [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities, Fair Value Disclosure	12.2	0.7
All Industries Other than Finance, Insurance and Real Estate [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Preferred Stock [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities, Fair Value Disclosure	11.8	12.3
All Industries Other than Finance, Insurance and Real Estate [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Common Stocks [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities, Fair Value Disclosure	0.6	0.4
All Industries Other than Finance, Insurance and Real Estate [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Preferred Stock [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities, Fair Value Disclosure	0.0	10.8
All Industries Other than Finance, Insurance and Real Estate [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Common Stocks [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities, Fair Value Disclosure	0.0	16.6
Limited Liability Companies and Limited Partnership Hedge Funds [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value Option Investments, Fair Value Disclosure		77.5
Limited Liability Companies and Limited Partnership Hedge Funds [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value Option Investments, Fair Value Disclosure		0.0
Limited Liability Companies and Limited Partnership Hedge Funds [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value Option Investments, Fair Value Disclosure		0.0
Limited Liability Companies and Limited Partnership Hedge Funds [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value Option Investments, Fair Value Disclosure		0.0
Fair Value, Inputs, Net Asset Value [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading Securities, Fair Value Disclosure		0.0
Cash Flow Hedge Derivative Instrument Assets at Fair Value		0.0
Investments, Fair Value Disclosure	229.1	246.0
Fair Value, Inputs, Net Asset Value [Member] | Fair Value, Measurements, Recurring [Member] | Investments in Fixed Maturities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities, Fair Value Disclosure	0.0	0.0
Fair Value, Inputs, Net Asset Value [Member] | Fair Value, Measurements, Recurring [Member] | U.S. Government and Government Agencies and Authorities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities, Fair Value Disclosure	0.0	0.0
Fair Value, Inputs, Net Asset Value [Member] | Fair Value, Measurements, Recurring [Member] | States and Political Subdivisions [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities, Fair Value Disclosure	0.0	0.0
Fair Value, Inputs, Net Asset Value [Member] | Fair Value, Measurements, Recurring [Member] | Foreign Governments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities, Fair Value Disclosure	0.0	0.0
Fair Value, Inputs, Net Asset Value [Member] | Fair Value, Measurements, Recurring [Member] | Corporate Bonds and Notes [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities, Fair Value Disclosure	0.0	0.0
Fair Value, Inputs, Net Asset Value [Member] | Fair Value, Measurements, Recurring [Member] | Redeemable Preferred Stocks
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities, Fair Value Disclosure		0.0
Fair Value, Inputs, Net Asset Value [Member] | Fair Value, Measurements, Recurring [Member] | Collateralized Loan Obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities, Fair Value Disclosure	0.0	0.0
Fair Value, Inputs, Net Asset Value [Member] | Fair Value, Measurements, Recurring [Member] | Other Mortgage- and Asset-backed
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities, Fair Value Disclosure	0.0	0.0
Fair Value, Inputs, Net Asset Value [Member] | Fair Value, Measurements, Recurring [Member] | Equity Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities, Fair Value Disclosure	229.1	168.5
Fair Value, Inputs, Net Asset Value [Member] | Fair Value, Measurements, Recurring [Member] | Exchange Traded Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities, Fair Value Disclosure	0.0	0.0
Fair Value, Inputs, Net Asset Value [Member] | Fair Value, Measurements, Recurring [Member] | Partnership Interest [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities, Fair Value Disclosure	229.1	168.5
Fair Value, Inputs, Net Asset Value [Member] | Finance, Insurance and Real Estate [Member] | Fair Value, Measurements, Recurring [Member] | Preferred Stock [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities, Fair Value Disclosure	0.0	0.0
Fair Value, Inputs, Net Asset Value [Member] | Finance, Insurance and Real Estate [Member] | Fair Value, Measurements, Recurring [Member] | Common Stocks [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities, Fair Value Disclosure	0.0	0.0
Fair Value, Inputs, Net Asset Value [Member] | All Industries Other than Finance, Insurance and Real Estate [Member] | Fair Value, Measurements, Recurring [Member] | Preferred Stock [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities, Fair Value Disclosure	0.0	0.0
Fair Value, Inputs, Net Asset Value [Member] | All Industries Other than Finance, Insurance and Real Estate [Member] | Fair Value, Measurements, Recurring [Member] | Common Stocks [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities, Fair Value Disclosure	$ 0.0	0.0
Fair Value, Inputs, Net Asset Value [Member] | Limited Liability Companies and Limited Partnership Hedge Funds [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value Option Investments, Fair Value Disclosure		$ 77.5