Pension and Postretirement Benefit Plans (Tables)

12 Months Ended

Dec. 31, 2015

Defined Benefit Pension Plans and Defined Benefit Postretirement Plans Disclosure [Abstract]

Summary of Pension and Postretirement Benefit Plans' Change in Benefit Obligation, Plan Assets and Funded Status

The following table sets forth information regarding the pension and postretirement benefit plans’ change in benefit obligation, plan assets and funded status at December 31, 2015 and 2014:

($ millions)	Pension						Postretirement
	2015			2014			2015			2014
Change in benefit obligation:
Benefit obligation at beginning of year	$	292.5		$	230.5		$	23.9		$	22.3
Service cost	7.7			4.6			—			—
Interest cost	11.1			10.8			0.9			1.1
Actuarial (gain) loss	(17.6		)	57.3			(3.3		)	1.7
Benefits paid	(12.4		)	(10.7		)	(1.2		)	(1.2		)
The Company’s portion of benefit obligation at end of year	$	281.3		$	292.5		$	20.3		$	23.9
Change in plan assets available for plan benefits:
Fair value of plan assets available for plan benefits at beginning of year	$	205.1		$	185.9		$	0.3		$	1.3
Employer contribution	13.0			13.0			—			—
Actual return on plan assets	(1.3		)	16.9			—			—
Benefits paid	(12.4		)	(10.7		)	(0.3		)	(1.0		)
The Company’s portion of fair value of plan assets at end of year	$	204.4		$	205.1		$	—		$	0.3
Supplemental executive retirement plan	(6.8		)	(6.3		)	—			—
Funded status at end of year	$	(83.7	)	$	(93.7	)	$	(20.3	)	$	(23.6	)
Accumulated benefit obligation end of year	$	263.1		$	260.1

Company's Share of Amounts Included in Accumulated Other Comprehensive Income (Loss)

The following table sets forth the Company’s share of the amounts included in accumulated other comprehensive income (loss) that have not been recognized in net periodic cost at December 31, 2015 and 2014:

($ millions)	2015			2014
Prior service benefit	$	(59.5	)	$	(64.9	)
Net actuarial loss	125.1			141.9
Total	$	65.6		$	77.0

Company's Share of Amortization Expected to be Recognized

The following table sets forth the Company’s share of amortization expected to be recognized for the year ending December 31, 2016:

($ millions)	2016
Prior service benefit	$	(5.4	)
Net actuarial loss	9.5
Total	$	4.1

Company's Share of Net Periodic Cost Components

The following table sets forth information regarding the Company’s share of pension and postretirement benefit plans’ components of net periodic cost for the years ended December 31, 2015, 2014 and 2013:

($ millions)	Pension									Postretirement
	2015			2014			2013			2015			2014			2013
Components of net periodic cost:
Service cost	$	7.9		$	5.2		$	6.1		$	—		$	—		$	0.4
Interest cost	11.3			11.1			9.6			1.1			1.1			1.2
Expected return on plan assets	(13.8		)	(12.6		)	(12.2		)	—			—			(0.2		)
Amortization of:
Prior service benefit	—			—			—			(5.4		)	(5.5		)	(5.5		)
Net actuarial loss	10.9			6.3			8.1			0.6			0.6			1.0
Net periodic cost (benefit)	$	16.3		$	10.0		$	11.6		$	(3.7	)	$	(3.8	)	$	(3.1	)

Company's Share of Expected Future Benefits Payments Schedule

The following table sets forth the Company’s share of the benefit payments, which reflect expected future service, expected to be paid:

($ millions)	Pension		Postretirement
2016	$	10.9	$	1.4
2017	11.2		1.5
2018	11.8		1.5
2019	12.2		1.4
2020	12.7		1.4
2021-2025	75.2		6.6

Weighted Average Assumptions Used to Determine Benefit Plans' Obligations

The following table sets forth the weighted average assumptions used to determine the benefit plans’ obligations at December 31, 2015 and 2014:

	Pension				Postretirement
	2015		2014		2015		2014
Benefit obligations weighted-average assumptions:
Discount rate	4.20	%	3.85	%	4.20	%	3.85	%
Rates of increase in compensation levels	3.50		3.50		—		—

Weighted Average Assumptions Used to Determine Benefit Plans' Net Periodic Cost

The following table sets forth the weighted average assumptions used to determine the benefit plans’ net periodic cost for the years ended December 31, 2015, 2014 and 2013:

	Pension						Postretirement
	2015		2014		2013		2015		2014		2013
Weighted-average assumptions:
Discount rate	3.85	%	4.85	%	4.05	%	3.85	%	4.85	%	4.05	%
Expected long-term rate of return on assets	7.00		7.00		7.50		—		—		7.50
Rates of increase in compensation levels	3.50		3.50		4.00		—		—		—

Schedule of Assumed Health Care Cost Trend Rates Used

The following table sets forth the assumed health care cost trend rates used for the years ended December 31, 2015, 2014 and 2013:

	Postretirement
	2015		2014		2013
Assumed health care cost trend rates:
Health care cost trend rate assumed for the next year	6.50	%	6.00	%	10.00	%
Rate to which the cost trend rate is assumed to decline (the ultimate trend rate)	3.80	%	3.80	%	5.00	%
Year that the rate reaches the ultimate trend rate	2076		2075		2018

Summary on Effective Impact of Assumed Health Care Cost Trend Rates on Amounts Reported for Postretirement Plan

The following table sets forth the effects of a one percentage point change in assumed health care cost trend rates for the year ended December 31, 2015:

($ millions)	Postretirement
	Increase		(Decrease)
One percentage point change:
Effect on total service and interest cost	$	0.1	$	0.1
Effect on accumulated postretirement benefit obligation	3.2		2.8

Summary of Asset Allocation Targets

The following table sets forth the asset allocation targets, as a percentage of total fair value, which are used as a guide by management when allocating funds as they become available.

	Asset allocation target (0 to 100%)
Asset Category:
Fixed maturity	49	%
U.S. large-cap equity	26
U.S. small-cap equity	11
International equity	10
Emerging market equity	4
Total	100	%

Company's Share of Pension Plan's Available-for-Sale Securities

The following tables set forth the Company’s share of pension plan’s available-for-sale securities within the fair value hierarchy at December 31, 2015 and 2014:

($ millions)	Total		Quoted prices in active markets for identical assets (Level 1)		Significant other observable inputs (Level 2)		Significant unobservable inputs (Level 3)
December 31, 2015
Fixed maturities:
U.S. treasury securities and obligations of U.S. government agencies	$	51.0	$	—	$	51.0	$	—
Corporate securities	38.9		—		38.9		—
U.S. government agencies mortgage-backed securities	6.4		—		6.4		—
Total fixed maturities	96.3		—		96.3		—
Equity securities:
Large-cap securities	59.0		59.0		—		—
Small-cap securities	22.3		22.3		—		—
Total equity securities	81.3		81.3		—		—
International instruments	18.6		—		18.6		—
Total pension plan investments	$	196.2	$	81.3	$	114.9	$	—

($ millions)	Total		Quoted prices in active markets for identical assets (Level 1)		Significant other observable inputs (Level 2)		Significant unobservable inputs (Level 3)
December 31, 2014
Fixed maturities:
U.S. treasury securities and obligations of U.S. government agencies	$	56.4	$	—	$	56.4	$	—
Corporate securities	39.7		—		39.7		—
U.S. government agencies mortgage-backed securities	9.4		—		9.4		—
Total fixed maturities	105.5		—		105.5		—
Equity securities:
Large-cap securities	53.7		53.7		—		—
Small-cap securities	21.8		21.8		—		—
Total equity securities	75.5		75.5		—		—
International instruments	18.7		—		18.7		—
Total pension plan investments	$	199.7	$	75.5	$	124.2	$	—

During 2015, the postretirement plan assets were sold in order to pay retiree medical costs. The following table sets forth the Company’s share of the postretirement plan’s available-for-sale securities within the fair value hierarchy at December 31, 2014:

($ millions)	Total		Quoted prices in active markets for identical assets (Level 1)		Significant other observable inputs (Level 2)		Significant unobservable inputs (Level 3)
December 31, 2014
Fixed maturities:
Corporate securities	$	0.1	$	—	$	0.1	$	—
Total fixed maturities	0.1		—		0.1		—
Short-term money market funds	0.2		0.2		—		—
Total postretirement plan investments	$	0.3	$	0.2	$	0.1	$	—