Fair Value Composition of Investment Portfolio by Major Security Type (Detail) - USD ($) $ in Millions		Sep. 30, 2016	Dec. 31, 2015	Sep. 30, 2015
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities	[1],[2]	$ 23,521.2	$ 20,937.3	$ 21,013.6
Long-Term Debt, Fair Value		3,505.2	2,887.8	2,899.2
Fixed maturities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		13,916.9	15,332.2	15,622.1
Fixed maturities | Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		7,729.3	8,860.8	8,925.0
Fixed maturities | Asset-backed Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		5,962.1	6,237.1	6,447.3
Fixed maturities | U.S. government obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		734.6	2,429.2	2,038.3
Fixed maturities | U.S. government obligations | Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		734.6	2,429.2	2,038.3
Fixed maturities | State and local government obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		2,566.0	2,721.4	3,067.9
Fixed maturities | State and local government obligations | Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		2,566.0	2,721.4	3,067.9
Fixed maturities | Foreign government obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		25.4	18.6	19.3
Fixed maturities | Foreign government obligations | Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		25.4	18.6	19.3
Fixed maturities | Corporate debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		4,403.3	3,691.6	3,799.5
Fixed maturities | Corporate debt securities | Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		4,403.3	3,691.6	3,799.5
Fixed maturities | Residential mortgage-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		1,594.2	1,726.7	1,809.4
Fixed maturities | Residential mortgage-backed securities | Asset-backed Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		1,594.2	1,726.7	1,809.4
Fixed maturities | Agency residential pass-through obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		44.1	89.3	111.9
Fixed maturities | Agency residential pass-through obligations | Asset-backed Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		44.1	89.3	111.9
Fixed maturities | Commercial mortgage-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		2,278.4	2,653.2	2,663.6
Fixed maturities | Commercial mortgage-backed securities | Asset-backed Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		2,278.4	2,653.2	2,663.6
Fixed maturities | Other asset-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		2,045.4	1,767.9	1,862.4
Fixed maturities | Other asset-backed securities | Asset-backed Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		2,045.4	1,767.9	1,862.4
Fixed maturities | Redeemable preferred stocks
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		225.5	234.3	249.8
Fixed maturities | Redeemable preferred stocks | Financials
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		95.7	92.0	88.1
Fixed maturities | Redeemable preferred stocks | Utilities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		30.4	51.2	56.0
Fixed maturities | Redeemable preferred stocks | Industrials
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		99.4	91.1	105.7
Equity securities | Nonredeemable preferred stocks
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		860.1	782.6	775.6
Equity securities | Nonredeemable preferred stocks | Financials
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		860.1	782.6	775.6
Equity securities | Common equities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		2,868.0	2,650.5	2,483.9
Equity securities | Common equities | Common equities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		2,867.6	2,650.2	2,483.6
Equity securities | Common equities | Other risk investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		0.4	0.3	0.3
Total Fixed Maturities and Equity Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		17,645.0	18,765.3	18,881.6
Short-term investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		5,876.2	2,172.0	2,132.0
Carrying (Reported) Amount, Fair Value Disclosure
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		21,886.9	19,688.4	19,811.0
Debt		3,153.9	2,707.9	2,714.3
Carrying (Reported) Amount, Fair Value Disclosure | Fixed maturities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		13,708.0	15,347.9	15,539.6
Carrying (Reported) Amount, Fair Value Disclosure | Fixed maturities | Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		7,587.8	8,834.8	8,869.9
Carrying (Reported) Amount, Fair Value Disclosure | Fixed maturities | Asset-backed Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		5,913.1	6,253.1	6,414.7
Carrying (Reported) Amount, Fair Value Disclosure | Fixed maturities | U.S. government obligations | Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		726.0	2,425.4	2,028.2
Carrying (Reported) Amount, Fair Value Disclosure | Fixed maturities | State and local government obligations | Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		2,508.9	2,677.6	3,025.0
Carrying (Reported) Amount, Fair Value Disclosure | Fixed maturities | Foreign government obligations | Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		25.4	18.6	19.3
Carrying (Reported) Amount, Fair Value Disclosure | Fixed maturities | Corporate debt securities | Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		4,327.5	3,713.2	3,797.4
Carrying (Reported) Amount, Fair Value Disclosure | Fixed maturities | Residential mortgage-backed securities | Asset-backed Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		1,582.6	1,726.0	1,801.8
Carrying (Reported) Amount, Fair Value Disclosure | Fixed maturities | Agency residential pass-through obligations | Asset-backed Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		43.6	90.3	112.2
Carrying (Reported) Amount, Fair Value Disclosure | Fixed maturities | Commercial mortgage-backed securities | Asset-backed Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		2,249.4	2,665.7	2,641.4
Carrying (Reported) Amount, Fair Value Disclosure | Fixed maturities | Other asset-backed securities | Asset-backed Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		2,037.5	1,771.1	1,859.3
Carrying (Reported) Amount, Fair Value Disclosure | Fixed maturities | Redeemable preferred stocks
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		207.1	260.0	255.0
Carrying (Reported) Amount, Fair Value Disclosure | Fixed maturities | Redeemable preferred stocks | Financials
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		77.1	76.8	71.8
Carrying (Reported) Amount, Fair Value Disclosure | Fixed maturities | Redeemable preferred stocks | Utilities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		30.6	65.1	65.1
Carrying (Reported) Amount, Fair Value Disclosure | Fixed maturities | Redeemable preferred stocks | Industrials
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		99.4	118.1	118.1
Carrying (Reported) Amount, Fair Value Disclosure | Equity securities | Nonredeemable preferred stocks
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		726.6	674.2	652.4
Carrying (Reported) Amount, Fair Value Disclosure | Equity securities | Nonredeemable preferred stocks | Financials
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		726.6	674.2	652.4
Carrying (Reported) Amount, Fair Value Disclosure | Equity securities | Common equities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		1,576.1	1,494.3	1,487.0
Carrying (Reported) Amount, Fair Value Disclosure | Equity securities | Common equities | Common equities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		1,575.7	1,494.0	1,486.7
Carrying (Reported) Amount, Fair Value Disclosure | Equity securities | Common equities | Other risk investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		0.4	0.3	0.3
Carrying (Reported) Amount, Fair Value Disclosure | Total Fixed Maturities and Equity Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		16,010.7	17,516.4	17,679.0
Carrying (Reported) Amount, Fair Value Disclosure | Short-term investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		5,876.2	2,172.0	2,132.0
Fair Value, Inputs, Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		8,833.7	7,309.2	6,706.9
Long-Term Debt, Fair Value		0.0	0.0	0.0
Fair Value, Inputs, Level 1 | Fixed maturities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		760.0	2,447.8	2,057.6
Fair Value, Inputs, Level 1 | Fixed maturities | Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		760.0	2,447.8	2,057.6
Fair Value, Inputs, Level 1 | Fixed maturities | Asset-backed Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		0.0	0.0	0.0
Fair Value, Inputs, Level 1 | Fixed maturities | U.S. government obligations | Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		734.6	2,429.2	2,038.3
Fair Value, Inputs, Level 1 | Fixed maturities | State and local government obligations | Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		0.0	0.0	0.0
Fair Value, Inputs, Level 1 | Fixed maturities | Foreign government obligations | Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		25.4	18.6	19.3
Fair Value, Inputs, Level 1 | Fixed maturities | Corporate debt securities | Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		0.0	0.0	0.0
Fair Value, Inputs, Level 1 | Fixed maturities | Residential mortgage-backed securities | Asset-backed Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		0.0	0.0	0.0
Fair Value, Inputs, Level 1 | Fixed maturities | Agency residential pass-through obligations | Asset-backed Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		0.0	0.0	0.0
Fair Value, Inputs, Level 1 | Fixed maturities | Commercial mortgage-backed securities | Asset-backed Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		0.0	0.0	0.0
Fair Value, Inputs, Level 1 | Fixed maturities | Other asset-backed securities | Asset-backed Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		0.0	0.0	0.0
Fair Value, Inputs, Level 1 | Fixed maturities | Redeemable preferred stocks
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		0.0	0.0	0.0
Fair Value, Inputs, Level 1 | Fixed maturities | Redeemable preferred stocks | Financials
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		0.0	0.0	0.0
Fair Value, Inputs, Level 1 | Fixed maturities | Redeemable preferred stocks | Utilities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		0.0	0.0	0.0
Fair Value, Inputs, Level 1 | Fixed maturities | Redeemable preferred stocks | Industrials
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		0.0	0.0	0.0
Fair Value, Inputs, Level 1 | Equity securities | Nonredeemable preferred stocks
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		154.6	154.9	158.7
Fair Value, Inputs, Level 1 | Equity securities | Nonredeemable preferred stocks | Financials
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		154.6	154.9	158.7
Fair Value, Inputs, Level 1 | Equity securities | Common equities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		2,867.6	2,650.2	2,483.6
Fair Value, Inputs, Level 1 | Equity securities | Common equities | Common equities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		2,867.6	2,650.2	2,483.6
Fair Value, Inputs, Level 1 | Equity securities | Common equities | Other risk investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		0.0	0.0	0.0
Fair Value, Inputs, Level 1 | Total Fixed Maturities and Equity Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		3,782.2	5,252.9	4,699.9
Fair Value, Inputs, Level 1 | Short-term investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		5,051.5	2,056.3	2,007.0
Fair Value, Inputs, Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		14,686.5	13,617.9	14,295.1
Long-Term Debt, Fair Value		3,371.6	2,722.9	2,727.5
Fair Value, Inputs, Level 2 | Fixed maturities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		13,156.3	12,874.5	13,553.2
Fair Value, Inputs, Level 2 | Fixed maturities | Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		6,969.3	6,413.0	6,866.4
Fair Value, Inputs, Level 2 | Fixed maturities | Asset-backed Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		5,961.5	6,227.2	6,437.0
Fair Value, Inputs, Level 2 | Fixed maturities | U.S. government obligations | Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		0.0	0.0	0.0
Fair Value, Inputs, Level 2 | Fixed maturities | State and local government obligations | Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		2,566.0	2,721.4	3,067.9
Fair Value, Inputs, Level 2 | Fixed maturities | Foreign government obligations | Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		0.0	0.0	0.0
Fair Value, Inputs, Level 2 | Fixed maturities | Corporate debt securities | Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		4,403.3	3,691.6	3,798.5
Fair Value, Inputs, Level 2 | Fixed maturities | Residential mortgage-backed securities | Asset-backed Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		1,594.2	1,726.7	1,809.4
Fair Value, Inputs, Level 2 | Fixed maturities | Agency residential pass-through obligations | Asset-backed Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		44.1	89.3	111.9
Fair Value, Inputs, Level 2 | Fixed maturities | Commercial mortgage-backed securities | Asset-backed Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		2,277.8	2,643.3	2,653.3
Fair Value, Inputs, Level 2 | Fixed maturities | Other asset-backed securities | Asset-backed Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		2,045.4	1,767.9	1,862.4
Fair Value, Inputs, Level 2 | Fixed maturities | Redeemable preferred stocks
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		225.5	234.3	249.8
Fair Value, Inputs, Level 2 | Fixed maturities | Redeemable preferred stocks | Financials
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		95.7	92.0	88.1
Fair Value, Inputs, Level 2 | Fixed maturities | Redeemable preferred stocks | Utilities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		30.4	51.2	56.0
Fair Value, Inputs, Level 2 | Fixed maturities | Redeemable preferred stocks | Industrials
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		99.4	91.1	105.7
Fair Value, Inputs, Level 2 | Equity securities | Nonredeemable preferred stocks
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		705.5	627.7	616.9
Fair Value, Inputs, Level 2 | Equity securities | Nonredeemable preferred stocks | Financials
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		705.5	627.7	616.9
Fair Value, Inputs, Level 2 | Equity securities | Common equities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		0.0	0.0	0.0
Fair Value, Inputs, Level 2 | Equity securities | Common equities | Common equities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		0.0	0.0	0.0
Fair Value, Inputs, Level 2 | Equity securities | Common equities | Other risk investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		0.0	0.0	0.0
Fair Value, Inputs, Level 2 | Total Fixed Maturities and Equity Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		13,861.8	13,502.2	14,170.1
Fair Value, Inputs, Level 2 | Short-term investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		824.7	115.7	125.0
Fair Value, Inputs, Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		1.0	10.2	11.6
Long-Term Debt, Fair Value		133.6	164.9	171.7
Fair Value, Inputs, Level 3 | Fixed maturities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		0.6	9.9	11.3
Fair Value, Inputs, Level 3 | Fixed maturities | Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		0.0	0.0	1.0
Fair Value, Inputs, Level 3 | Fixed maturities | Asset-backed Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		0.6	9.9	10.3
Fair Value, Inputs, Level 3 | Fixed maturities | U.S. government obligations | Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		0.0	0.0	0.0
Fair Value, Inputs, Level 3 | Fixed maturities | State and local government obligations | Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		0.0	0.0	0.0
Fair Value, Inputs, Level 3 | Fixed maturities | Foreign government obligations | Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		0.0	0.0	0.0
Fair Value, Inputs, Level 3 | Fixed maturities | Corporate debt securities | Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		0.0	0.0	1.0
Fair Value, Inputs, Level 3 | Fixed maturities | Residential mortgage-backed securities | Asset-backed Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		0.0	0.0	0.0
Fair Value, Inputs, Level 3 | Fixed maturities | Agency residential pass-through obligations | Asset-backed Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		0.0	0.0	0.0
Fair Value, Inputs, Level 3 | Fixed maturities | Commercial mortgage-backed securities | Asset-backed Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		0.6	9.9	10.3
Fair Value, Inputs, Level 3 | Fixed maturities | Other asset-backed securities | Asset-backed Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		0.0	0.0	0.0
Fair Value, Inputs, Level 3 | Fixed maturities | Redeemable preferred stocks
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		0.0	0.0	0.0
Fair Value, Inputs, Level 3 | Fixed maturities | Redeemable preferred stocks | Financials
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		0.0	0.0	0.0
Fair Value, Inputs, Level 3 | Fixed maturities | Redeemable preferred stocks | Utilities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		0.0	0.0	0.0
Fair Value, Inputs, Level 3 | Fixed maturities | Redeemable preferred stocks | Industrials
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		0.0	0.0	0.0
Fair Value, Inputs, Level 3 | Equity securities | Nonredeemable preferred stocks
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		0.0	0.0	0.0
Fair Value, Inputs, Level 3 | Equity securities | Nonredeemable preferred stocks | Financials
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		0.0	0.0	0.0
Fair Value, Inputs, Level 3 | Equity securities | Common equities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		0.4	0.3	0.3
Fair Value, Inputs, Level 3 | Equity securities | Common equities | Common equities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		0.0	0.0	0.0
Fair Value, Inputs, Level 3 | Equity securities | Common equities | Other risk investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		0.4	0.3	0.3
Fair Value, Inputs, Level 3 | Total Fixed Maturities and Equity Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		1.0	10.2	11.6
Fair Value, Inputs, Level 3 | Short-term investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		$ 0.0	$ 0.0	$ 0.0

[1] Our portfolio reflects the effect of unsettled security transactions and collateral on open derivative positions; at September 30, 2016 and 2015, $185.3 million and $149.9 million, respectively, were included in "other liabilities" and $23.1 million was in "other assets" at December 31, 2015.

[2] The total fair value of the portfolio at September 30, 2016 and 2015, and December 31, 2015 included $1.0 billion, $1.0 billion, and $1.3 billion, respectively, of securities held in a consolidated, non-insurance subsidiary of the holding company, net of any unsettled security transactions.