Investments (Tables)

12 Months Ended

Dec. 31, 2017

Notes to Financial Statements [Abstract]

Amortized Cost and Fair Values of Securities by Security Type

At December 31, 2017 and 2016, all fixed maturity securities were classified as available-for-sale. The amortized cost and fair values of securities by security type are shown as follows:

	December 31, 2017
	Amortized Cost		Gross Unrealized Gain		Gross Unrealized Loss		Fair Value
	(in millions of dollars)
United States Government and Government Agencies and Authorities	$	1,311.1	$	176.1	$	4.7	$	1,482.5
States, Municipalities, and Political Subdivisions	1,942.8		395.4		1.3		2,336.9
Foreign Governments	673.0		191.3		0.4		863.9
Public Utilities	6,952.7		1,296.4		12.6		8,236.5
Mortgage/Asset-Backed Securities	1,873.2		105.1		4.7		1,973.6
All Other Corporate Bonds	26,988.7		3,633.5		99.8		30,522.4
Redeemable Preferred Stocks	39.0		3.0		—		42.0
Total Fixed Maturity Securities	$	39,780.5	$	5,800.8	$	123.5	$	45,457.8

	December 31, 2016
	Amortized Cost		Gross Unrealized Gain		Gross Unrealized Loss		Fair Value
	(in millions of dollars)
United States Government and Government Agencies and Authorities	$	1,202.8	$	183.1	$	3.5	$	1,382.4
States, Municipalities, and Political Subdivisions	1,868.0		294.8		4.8		2,158.0
Foreign Governments	714.8		199.9		—		914.7
Public Utilities	6,916.1		1,123.5		16.9		8,022.7
Mortgage/Asset-Backed Securities	2,104.9		134.7		9.2		2,230.4
All Other Corporate Bonds	26,707.1		2,944.0		183.9		29,467.2
Redeemable Preferred Stocks	39.0		3.2		0.3		41.9
Total Fixed Maturity Securities	$	39,552.7	$	4,883.2	$	218.6	$	44,217.3

Length of Time Fixed Maturity Securities had been in a Gross Unrealized Loss Position

The following charts indicate the length of time our fixed maturity securities have been in a gross unrealized loss position.

	December 31, 2017
	Less Than 12 Months				12 Months or Greater
	Fair Value		Gross Unrealized Loss		Fair Value		Gross Unrealized Loss
	(in millions of dollars)
United States Government and Government Agencies and Authorities	$	157.9	$	3.0	$	58.8	$	1.8
States, Municipalities, and Political Subdivisions	45.7		0.5		22.3		0.7
Foreign Governments	13.2		0.4		—		—
Public Utilities	213.2		7.9		133.5		4.7
Mortgage/Asset-Backed Securities	252.5		1.4		144.7		3.3
All Other Corporate Bonds	1,355.1		26.8		785.2		73.0
Total Fixed Maturity Securities	$	2,037.6	$	40.0	$	1,144.5	$	83.5

	December 31, 2016
	Less Than 12 Months				12 Months or Greater
	Fair Value		Gross Unrealized Loss		Fair Value		Gross Unrealized Loss
	(in millions of dollars)
United States Government and Government Agencies and Authorities	$	132.8	$	3.5	$	—	$	—
States, Municipalities, and Political Subdivisions	132.2		4.8		—		—
Public Utilities	260.2		15.3		15.6		1.6
Mortgage/Asset-Backed Securities	513.2		9.1		0.8		0.1
All Other Corporate Bonds	3,621.0		122.1		774.7		61.8
Redeemable Preferred Stocks	7.9		0.1		10.8		0.2
Total Fixed Maturity Securities	$	4,667.3	$	154.9	$	801.9	$	63.7

Distribution of the Maturity Dates for Fixed Maturity Securities

The following is a distribution of the maturity dates for fixed maturity securities. The maturity dates have not been adjusted for possible calls or prepayments.

	December 31, 2017
	Total Amortized Cost		Unrealized Gain Position				Unrealized Loss Position
			Gross Gain		Fair Value		Gross Loss		Fair Value
	(in millions of dollars)
1 year or less	$	1,625.1	$	30.9	$	1,638.8	$	3.1	$	14.1
Over 1 year through 5 years	5,579.9		453.6		5,810.9		18.5		204.1
Over 5 years through 10 years	12,091.1		1,169.8		11,916.5		53.2		1,291.2
Over 10 years	18,611.2		4,041.4		21,333.1		44.0		1,275.5
	37,907.3		5,695.7		40,699.3		118.8		2,784.9
Mortgage/Asset-Backed Securities	1,873.2		105.1		1,576.4		4.7		397.2
Total Fixed Maturity Securities	$	39,780.5	$	5,800.8	$	42,275.7	$	123.5	$	3,182.1

	December 31, 2016
	Total Amortized Cost		Unrealized Gain Position				Unrealized Loss Position
			Gross Gain		Fair Value		Gross Loss		Fair Value
	(in millions of dollars)
1 year or less	$	1,338.8	$	28.6	$	1,355.6	$	—	$	11.8
Over 1 year through 5 years	6,231.0		553.5		6,605.6		8.2		170.7
Over 5 years through 10 years	10,991.6		843.8		9,336.2		82.8		2,416.4
Over 10 years	18,886.4		3,322.6		19,734.3		118.4		2,356.3
	37,447.8		4,748.5		37,031.7		209.4		4,955.2
Mortgage/Asset-Backed Securities	2,104.9		134.7		1,716.4		9.2		514.0
Total Fixed Maturity Securities	$	39,552.7	$	4,883.2	$	38,748.1	$	218.6	$	5,469.2

Low Income Housing Tax Credits

The Company invests in tax credit partnerships primarily for the receipt of income tax credits and tax benefits derived from passive losses on the investments. Amounts recognized in the consolidated statements of income are as follows:

	Year Ended December 31
	2017			2016			2015
	(in millions of dollars)
Income Tax Credits	$	41.8		$	41.8		$	41.8
Amortization, Net of Tax	(23.2		)	(23.2		)	(23.3		)
Income Tax Benefit	$	18.6		$	18.6		$	18.5

Mortgage Loans by Property Type and Geographic Region

Mortgage loans by property type and geographic region are presented below.

	December 31
	2017				2016
	(in millions of dollars)
	Carrying		Percent of		Carrying		Percent of
	Amount		Total		Amount		Total
Property Type
Apartment	$	360.0	16.3	%	$	288.4	14.1	%
Industrial	601.2		27.2		573.6		28.1
Office	692.3		31.3		700.1		34.4
Retail	527.6		23.8		455.4		22.4
Other	32.1		1.4		21.4		1.0
Total	$	2,213.2	100.0	%	$	2,038.9	100.0	%

Region
New England	$	56.1	2.5	%	$	72.7	3.6	%
Mid-Atlantic	155.5		7.0		125.3		6.1
East North Central	282.0		12.8		230.1		11.3
West North Central	210.1		9.5		172.0		8.4
South Atlantic	494.4		22.3		438.3		21.5
East South Central	88.8		4.0		91.6		4.5
West South Central	247.4		11.2		268.7		13.2
Mountain	251.2		11.4		214.1		10.5
Pacific	427.7		19.3		426.1		20.9
Total	$	2,213.2	100.0	%	$	2,038.9	100.0	%

Mortgage Loans by Credit Quality Indicators

Mortgage loans, sorted by the applicable credit quality indicators, are as follows:

	December 31
	2017		2016
	(in millions of dollars)
Internal Rating
Aa	$	0.4	$	0.7
A	445.7		488.2
Baa	1,753.0		1,506.6
Ba	14.1		43.4
Total	$	2,213.2	$	2,038.9

Loan-to-Value Ratio
<= 65%	$	1,101.7	$	917.9
> 65% <= 75%	1,041.6		1,011.5
> 75% <= 85%	49.3		50.8
> 85%	20.6		58.7
Total	$	2,213.2	$	2,038.9

Remaining Contractual Maturity of Securities Lending Agreements

The remaining contractual maturities of our securities lending agreements disaggregated by class of collateral pledged are as follows:

	December 31
	2017		2016
	Overnight and Continuous
	(in millions of dollars)
United States Government and Government Agencies and Authorities	$	0.2	$	0.1
Public Utilities	0.5		0.1
All Other Corporate Bonds	29.8		29.7
Total Borrowings	30.5		29.9
Gross Amount of Recognized Liability for Securities Lending Transactions	30.5		29.9
Amounts Related to Agreements Not Included in Offsetting Disclosure Contained Herein	$	—	$	—

Schedule of Financial Instrument and Derivative Offsetting

Shown below are our financial instruments that either meet the accounting requirements that allow them to be offset in our balance sheets or that are subject to an enforceable master netting arrangement or similar agreement. Our accounting policy is to not offset these financial instruments in our balance sheets. Net amounts disclosed below have been reduced by the amount of collateral pledged to or received from our counterparties.

	December 31, 2017
	Gross Amount						Gross Amount Not
	of Recognized		Gross Amount		Net Amount		Offset in Balance Sheet
	Financial		Offset in		Presented in		Financial			Cash			Net
	Instruments		Balance Sheet		Balance Sheet		Instruments			Collateral			Amount
	(in millions of dollars)
Financial Assets:
Derivatives	$	19.5	$	—	$	19.5	$	(4.2	)	$	(15.3	)	$	—
Securities Lending	159.2		—		159.2		(128.7		)	(30.5		)	—
Total	$	178.7	$	—	$	178.7	$	(132.9	)	$	(45.8	)	$	—
Financial Liabilities:
Derivatives	$	52.2	$	—	$	52.2	$	(42.9	)	$	—		$	9.3
Securities Lending	30.5		—		30.5		(30.5		)	—			—
Total	$	82.7	$	—	$	82.7	$	(73.4	)	$	—		$	9.3

	December 31, 2016
	Gross Amount						Gross Amount Not
	of Recognized		Gross Amount		Net Amount		Offset in Balance Sheet
	Financial		Offset in		Presented in		Financial			Cash			Net
	Instruments		Balance Sheet		Balance Sheet		Instruments			Collateral			Amount
	(in millions of dollars)
Financial Assets:
Derivatives	$	32.7	$	—	$	32.7	$	(7.3	)	$	(25.4	)	$	—
Securities Lending	178.5		—		178.5		(148.6		)	(29.9		)	—
Total	$	211.2	$	—	$	211.2	$	(155.9	)	$	(55.3	)	$	—
Financial Liabilities:
Derivatives	$	52.8	$	—	$	52.8	$	(37.6	)	$	—		$	15.2
Securities Lending	29.9		—		29.9		(29.9		)	—			—
Total	$	82.7	$	—	$	82.7	$	(67.5	)	$	—		$	15.2

Net Investment Income

Net Investment Income

Net investment income reported in our consolidated statements of income is as follows:

	Year Ended December 31
	2017		2016		2015
	(in millions of dollars)
Fixed Maturity Securities	$	2,271.8	$	2,293.9	$	2,327.1
Derivatives	56.4		49.8		44.2
Mortgage Loans	104.2		114.0		114.0
Policy Loans	17.9		17.3		16.7
Other Long-term Investments	37.0		22.6		21.6
Short-term Investments	11.3		7.5		3.4
Gross Investment Income	2,498.6		2,505.1		2,527.0
Less Investment Expenses	32.8		31.9		31.2
Less Investment Income on Participation Fund Account Assets	14.1		14.2		14.6
Net Investment Income	$	2,451.7	$	2,459.0	$	2,481.2

Realized Investment Gains and Losses Reported in Consolidated Statements of Income

Realized Investment Gain and Loss

Realized investment gains and losses are as follows:

	Year Ended December 31
	2017			2016			2015
	(in millions of dollars)
Fixed Maturity Securities
Gross Gains on Sales	$	13.8		$	34.3		$	23.8
Gross Losses on Sales	(4.4		)	(17.2		)	(25.6		)
Other-Than-Temporary Impairment Loss	(8.1		)	(30.5		)	(32.4		)
Mortgage Loans and Other Invested Assets
Gross Gains on Sales	9.4			5.5			16.0
Gross Losses on Sales	(0.2		)	(0.7		)	(0.1		)
Impairment Loss	(0.9		)	(5.7		)	(5.9		)
Embedded Derivative in Modified Coinsurance Arrangement	30.8			40.9			(37.7		)
All Other Derivatives	(0.1		)	(1.5		)	35.7
Foreign Currency Transactions	—			(0.9		)	(17.6		)
Net Realized Investment Gain (Loss)	$	40.3		$	24.2		$	(43.8	)