Investments (Tables)

12 Months Ended

Dec. 31, 2012

Notes to Financial Statements [Abstract]

Schedule of Available-for-sale Securities Reconciliation

At December 31, 2012 and 2011, 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, 2012
	Amortized Cost		Gross Unrealized Gain		Gross Unrealized Loss		Fair Value
	(in millions of dollars)
United States Government and Government Agencies and Authorities	$	1,020.9	$	329.0	$	1.1	$	1,348.8
States, Municipalities, and Political Subdivisions	1,498.4		316.2		7.8		1,806.8
Foreign Governments	1,280.4		226.6		—		1,507.0
Public Utilities	9,294.3		1,865.0		15.1		11,144.2
Mortgage/Asset-Backed Securities	1,927.9		289.1		0.5		2,216.5
All Other Corporate Bonds	22,696.6		4,245.3		31.5		26,910.4
Redeemable Preferred Stocks	33.0		6.3		—		39.3
Total Fixed Maturity Securities	$	37,751.5	$	7,277.5	$	56.0	$	44,973.0

	December 31, 2011
	Amortized Cost		Gross Unrealized Gain		Gross Unrealized Loss		Fair Value
	(in millions of dollars)
United States Government and Government Agencies and Authorities	$	1,005.8	$	299.7	$	1.1	$	1,304.4
States, Municipalities, and Political Subdivisions	1,377.8		222.6		8.8		1,591.6
Foreign Governments	1,139.4		237.3		—		1,376.7
Public Utilities	9,015.7		1,646.2		28.6		10,633.3
Mortgage/Asset-Backed Securities	2,634.6		344.1		5.5		2,973.2
All Other Corporate Bonds	21,411.6		3,314.8		176.3		24,550.1
Redeemable Preferred Stocks	55.8		3.5		1.9		57.4
Total Fixed Maturity Securities	$	36,640.7	$	6,068.2	$	222.2	$	42,486.7

As of December 31, 2012 and 2011, we held no fixed maturity securities for which a portion of an other-than-temporary impairment had previously been recognized in other comprehensive income.

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, 2012
	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	$	—	$	—	$	6.5	$	1.1
States, Municipalities, and Political Subdivisions	30.8		0.9		42.1		6.9
Public Utilities	110.3		3.9		147.6		11.2
Mortgage/Asset-Backed Securities	4.4		—		3.8		0.5
All Other Corporate Bonds	441.3		7.0		396.8		24.5
Total Fixed Maturity Securities	$	586.8	$	11.8	$	596.8	$	44.2

	December 31, 2011
	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	$	—	$	—	$	6.3	$	1.1
States, Municipalities, and Political Subdivisions	51.6		1.3		75.3		7.5
Public Utilities	192.0		7.9		142.2		20.7
Mortgage/Asset-Backed Securities	94.2		4.8		19.6		0.7
All Other Corporate Bonds	1,703.9		65.5		684.9		110.8
Redeemable Preferred Stocks	—		—		20.9		1.9
Total Fixed Maturity Securities	$	2,041.7	$	79.5	$	949.2	$	142.7

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, 2012
	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	$	956.4	$	21.2	$	934.1	$	0.5	$	43.0
Over 1 year through 5 years	5,922.8		628.1		6,449.8		5.0		96.1
Over 5 years through 10 years	9,752.3		1,606.4		10,997.0		7.6		354.1
Over 10 years	19,192.1		4,732.7		23,200.2		42.4		682.2
	35,823.6		6,988.4		41,581.1		55.5		1,175.4
Mortgage/Asset-Backed Securities	1,927.9		289.1		2,208.3		0.5		8.2
Total Fixed Maturity Securities	$	37,751.5	$	7,277.5	$	43,789.4	$	56.0	$	1,183.6

	December 31, 2011
	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	$	715.1	$	16.0	$	701.4	$	0.1	$	29.6
Over 1 year through 5 years	5,161.5		449.8		4,949.0		20.7		641.6
Over 5 years through 10 years	9,630.5		1,266.3		9,903.8		52.8		940.2
Over 10 years	18,499.0		3,992.0		21,082.2		143.1		1,265.7
	34,006.1		5,724.1		36,636.4		216.7		2,877.1
Mortgage/Asset-Backed Securities	2,634.6		344.1		2,859.4		5.5		113.8
Total Fixed Maturity Securities	$	36,640.7	$	6,068.2	$	39,495.8	$	222.2	$	2,990.9

Credit Losses Remaining in Retained Earnings Related to Adoption of Accounting Standard

The following table presents the before-tax credit related portion of an other-than-temporary impairment on a fixed maturity security still held for the periods shown for which a portion of the other-than-temporary impairment was recognized in other comprehensive income. This fixed maturity security was sold during 2011. We held no fixed maturity securities during 2012 for which a portion of an other-than-temporary impairment was recognized in other comprehensive income.

	Year Ended December 31
	2012		2011			2010
	(in millions of dollars)
Balance at Beginning of Year	$	—	$	8.5		$	18.3
Sales or Maturities of Securities	—		(8.5		)	(9.8		)
Balance at End of Year	$	—	$	—		$	8.5

Mortgage Loans by Property Type

Mortgage loans by property type and geographic region are as follows:

	December 31
	2012				2011
	(in millions of dollars)
	Carrying		Percent of		Carrying		Percent of
	Amount		Total		Amount		Total
Property Type
Apartment	$	34.0	2.0	%	$	28.0	1.8	%
Industrial	513.4		30.0		502.0		31.1
Mixed	78.4		4.6		93.5		5.8
Office	713.4		41.6		659.3		40.9
Retail	373.5		21.8		322.4		20.0
Other	—		—		7.1		0.4
Total	$	1,712.7	100.0	%	$	1,612.3	100.0	%

Mortgage Loans by Geographic Region

Region
New England	$	114.3	6.7	%	$	147.0	9.1	%
Mid-Atlantic	160.0		9.3		174.1		10.8
East North Central	224.7		13.1		212.7		13.2
West North Central	160.8		9.4		151.2		9.4
South Atlantic	440.9		25.7		383.8		23.8
East South Central	79.6		4.7		52.4		3.3
West South Central	159.5		9.3		160.4		9.9
Mountain	90.5		5.3		69.5		4.3
Pacific	282.4		16.5		261.2		16.2
Total	$	1,712.7	100.0	%	$	1,612.3	100.0	%

Mortgage Loans, Sorted by Applicable Credit Quality Indicators, Internal Rating

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

	December 31
	2012		2011
	(in millions of dollars)
Internal Rating
Aa	$	11.5	$	10.9
A	659.4		712.6
Baa	994.5		855.0
Ba	34.2		20.7
B	13.1		13.1
Total	$	1,712.7	$	1,612.3

Mortgage Loans, Sorted by Applicable Credit Quality Indicators, Loan to Value Ratio

Loan-to-Value Ratio
<= 65%	$	624.7	$	578.4
> 65% <= 75%	858.8		802.3
> 75% <= 85%	142.5		165.1
> 85%	86.7		66.5
Total	$	1,712.7	$	1,612.3

Activity in the Allowance for Credit Losses

The activity in the allowance for credit losses is as follows:

	Year Ended December 31
	2012			2011		2010
	(in millions of dollars)
Balance at Beginning of Year	$	1.5		$	1.5	$	3.2
Provision	1.8			—		2.4
Charge-offs, Net of Recoveries	(1.8		)	—		(4.1		)
Balance at End of Year	$	1.5		$	1.5	$	1.5

Impaired Mortgage Loans

Impaired mortgage loans are as follows:

	December 31, 2012
	(in millions of dollars)
			Unpaid
	Recorded		Principal		Related
	Investment		Balance		Allowance
With No Related Allowance Recorded	$	4.3	$	4.3	$	—
With an Allowance Recorded	13.1		14.6		1.5
Total	$	17.4	$	18.9	$	1.5
	December 31, 2011
	(in millions of dollars)
			Unpaid
	Recorded		Principal		Related
	Investment		Balance		Allowance
With No Related Allowance Recorded	$	9.4	$	9.4	$	—
With an Allowance Recorded	13.1		14.6		1.5
Total	$	22.5	$	24.0	$	1.5

Troubled Debt Restructurings on Financing Receivables [Table Text Block]

A summary of our troubled debt restructurings is as follows:

	Year Ended December 31
	2012		2011		2010
	(in millions of dollars)
Foreclosure
Carrying Amount	$	17.3	$	19.9	$	7.2
Number of Loans	3		2		1
Payoff/Sale
Carrying Amount	$	—	$	3.2	$	4.7
Realized Loss	$	—	$	0.2	$	1.4
Number of Loans	—		1		3

We had no realized losses on loan foreclosures for the years ended December 31, 2012, 2011, and 2010 other than the initial impairment losses recognized prior to foreclosure.

Investment Income [Table Text Block]

Net Investment Income

	Year Ended December 31
	2012		2011		2010
	(in millions of dollars)
Fixed Maturity Securities	$	2,404.0	$	2,425.2	$	2,401.9
Derivative Financial Instruments	28.9		22.9		17.2
Mortgage Loans	107.1		100.1		91.1
Policy Loans	14.8		14.1		13.9
Other Long-term Investments	15.2		13.1		18.5
Short-term Investments	4.3		2.9		3.2
Gross Investment Income	2,574.3		2,578.3		2,545.8
Less Investment Expenses	26.9		26.9		28.2
Less Investment Income on PFA Assets	16.1		17.4		18.8
Less Amortization of Tax Credit Partnerships	16.1		14.4		3.3
Net Investment Income	$	2,515.2	$	2,519.6	$	2,495.5

Realized Investment Gains and Losses Reported in Consolidated Statements of Income

Realized Investment Gain and Loss

Realized investment gains and losses reported in our consolidated statements of income are as follows:

	Year Ended December 31
	2012			2011			2010
	(in millions of dollars)
Fixed Maturity Securities
Gross Gains on Sales	$	29.3		$	74.0		$	61.1
Gross Losses on Sales	(20.4		)	(24.0		)	(41.3		)
Other-Than-Temporary Impairment Loss	—			(19.9		)	(15.9		)
Mortgage Loans and Other Invested Assets
Gross Gains on Sales	5.0			7.1			7.9
Gross Losses on Sales	(4.3		)	(0.5		)	(0.5		)
Impairment Loss	(1.9		)	(0.6		)	(3.8		)
Embedded Derivative in Modified Coinsurance Arrangement	51.8			(39.4		)	21.1
Foreign Currency Transactions	(3.3		)	(1.6		)	(3.9		)
Net Realized Investment Gain (Loss)	$	56.2		$	(4.9	)	$	24.7