Retirement Benefits (Tables)

12 Months Ended

Dec. 31, 2020

Retirement Benefits [Abstract]

Summary of Company's Plan Assets, Benefit Obligations, and Funded Status

Assets, benefit obligations, and the funded status of the plans were determined at December 31, 2020 and 2019.

	Pension Benefits				Medical and Life Insurance Benefits
	As of December 31,
	2020		2019		2020		2019
	(In millions)
Change in fair value of assets:
Fair value - beginning of year	$	932.5	$	894.8	$	—	$	—
Gain (loss) on assets	117.1		144.8		—		—
Employer contributions	15.6		1.4		2.8		3.1
Benefits paid (1)	(108.2)		(108.5)		(2.8)		(3.1)
Fair value - end of year	$	957.0	$	932.5	$	—	$	—
Change in benefit obligation:
Benefit obligation - beginning of year	$	1,349.8	$	1,288.7	$	25.9	$	31.3
Interest cost	42.5		52.7		0.8		1.2
Actuarial losses (gains)	97.4		116.9		1.1		(3.5)
Benefits paid	(108.2)		(108.5)		(2.8)		(3.1)
Benefit obligation and accumulated benefit obligation - end of year	$	1,381.5	$	1,349.8	$	25.0	$	25.9
Funded status of the plans	$	(424.5)	$	(417.3)	$	(25.0)	$	(25.9)
Amounts recognized in the consolidated balance sheets:
Postretirement medical and life insurance benefits, current	$	—	$	—	$	(3.5)	$	(3.6)
Postretirement medical and life insurance benefits, noncurrent	—		—		(21.5)		(22.3)
Pension liability, non-qualified current (component of other current liabilities)	(1.3)		(1.3)		—		—
Pension liability, non-qualified (component of other noncurrent liabilities)	(18.0)		(17.1)		—		—
Pension benefits, noncurrent	(405.2)		(398.9)		—		—
Net liability recognized in the consolidated balance sheets	$	(424.5)	$	(417.3)	$	(25.0)	$	(25.9)

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(1)Benefits paid for medical and life insurance benefits are net of the Medicare Part D Subsidy of $0.1 million received in both 2020 and 2019.

Summary of Components of Retirement Benefit Expense (Income)

The following table presents the components of retirement benefits expense (income): 

	Pension Benefits						Medical and Life Insurance Benefits
	Year Ended December 31,						Year Ended December 31,
	2020		2019		2018		2020		2019		2018
	(In millions)
Interest cost on benefit obligation	$	42.5	$	52.7	$	49.7	$	0.8	$	1.2	$	1.2
Assumed return on assets	(60.5)		(64.8)		(60.1)		—		—		—
Amortization of prior service costs (credits)	0.1		0.1		0.1		—		(0.2)		(0.2)
Amortization of net losses (gains)	57.4		40.9		70.7		(3.7)		(3.8)		(3.8)
	$	39.5	$	28.9	$	60.4	$	(2.9)	$	(2.8)	$	(2.8)

The following table presents the actual return and rate of return on assets:

	Year Ended December 31,
	2020			2019			2018
	(In millions, except rate of return)
Actual gain (loss) on assets	$	117.1		$	144.8		$	(57.8)
Actual rate of return (loss) on assets	15.6		%	18.0		%	(5.2)		%

Schedule of Assumptions Used to Determine Benefit Obligations

The following table presents the assumptions, calculated based on a weighted-average, to determine the benefit obligations:

	Pension Benefits				Medical and Life Insurance Benefits
	As of December 31,				As of December 31,
	2020		2019		2020		2019
Discount rate	2.52	%	3.28	%	2.28	%	3.19	%
Discount rate (non-qualified plan)	2.51	%	3.30	%	*		*
Ultimate healthcare trend rate	*		*		4.50	%	4.50	%
Initial healthcare trend rate (pre 65/post 65)	*		*		6.50	%	5.50	%
Year ultimate rate attained (pre 65/post 65)	*		*		2028		2022

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*    Not applicable

Schedule of Assumptions Used to Determine Periodic Benefit Expense (Income)

The following table presents the assumptions, calculated based on a weighted-average, to determine the retirement benefits expense (income):

	Pension Benefits					Medical and Life Insurance Benefits
	Year Ended December 31,					Year Ended December 31,
	2020	2019		2018		2020	2019		2018
Discount rate	3.28 %	4.27	%	3.59	%	3.19 %	4.09	%	3.37	%
Discount rate (non-qualified plan)	3.30 %	4.27	%	3.62	%	*	*		*
Expected long-term rate of return on assets	7.00 %	7.00	%	7.00	%	*	*		*
Ultimate healthcare trend rate	*	*		*		4.50 %	4.50	%	5.00	%
Initial healthcare trend rate (pre 65/post 65)	*	*		*		5.50 %	6.00	%	6.50	%
Year ultimate rate attained (pre 65/post 65)	*	*		*		2022	2022		2021

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*    Not applicable

Schedule of Pension Plan's Asset Allocations by Asset Category

The following table presents the asset allocations by asset category:

	As of December 31,
	2020		2019
Cash and cash equivalents	2	%	4	%
Equity securities	46		44
Fixed income	15		15
Registered investment companies	2		2
Private assets	11		12
Hedge funds	24		23
Total	100	%	100	%

Schedule of Fair Value of Pension Plan Assets and Liabilities by Asset Category and by Level

The following tables present the fair value by asset category and by level:

	Total		Quoted Prices in Active Markets for Identical Assets (Level 1)		Other Observable Inputs (Level 2)		Unobservable Inputs (Level 3)
	(In millions)
December 31, 2020
Equity securities:
Domestic equity securities	$	406.3	$	400.2	$	—	$	6.1
International equity securities	37.0		37.0		—		—
Fixed income:
Corporate debt securities	71.5		—		39.6		31.9
Asset-backed securities	28.7		—		28.7		—
U.S. government securities	41.4		—		41.4		—
Municipal bonds	0.6		—		0.6		—
Foreign bonds	0.5		—		0.5		—
Registered investment companies	16.4		16.4		—		—
Private assets	3.1		—		—		3.1
Total	605.5		$	453.6	$	110.8	$	41.1
Investment measured at Net Asset Value ("NAV")
Private assets	100.8
Hedge funds	232.3
Common/collective trusts ("CCTs")	36.2
Total investments measured at NAV	369.3
Receivables	0.8
Payables	(18.6)
Total assets	$	957.0

	Total		Quoted Prices in Active Markets for Identical Assets (Level 1)		Other Observable Inputs (Level 2)		Unobservable Inputs (Level 3)
	(In millions)
December 31, 2019
Cash and cash equivalents	$	0.1	$	0.1	$	—	$	—
Equity securities:
Domestic equity securities	372.6		368.4		—		4.2
International equity securities	33.5		33.5		—		—
Fixed income:
Corporate debt securities	78.2		—		50.6		27.6
Asset-backed securities	26.3		—		26.3		—
U.S. government securities	31.3		—		31.3		—
Foreign bonds	0.8		—		0.8		—
Foreign exchange contracts	0.1		—		0.1		—
Registered investment companies	22.8		22.8		—		—
Private assets	5.4		—		—		5.4
Total	571.1		$	424.8	$	109.1	$	37.2
Investment measured at NAV
Private assets	106.3
Hedge funds	218.7
CCTs	50.0
Total investments measured at NAV	375.0
Receivables	6.5
Payables	(20.1)
Total assets	$	932.5

Schedule of Changes in Fair Value of Level 3 Investments

The following tables present the changes in the fair value of the Level 3 investments:

	December 31, 2019		Unrealized Gains (Losses)		Realized Gains		Purchases, Sales, and Settlements, net		December 31, 2020
	(In millions)
Equity securities:
Domestic equity securities	$	4.2	$	1.9	$	—	$	—	$	6.1
Corporate debt securities	27.6		5.4		—		(1.1)		31.9
Private assets	5.4		1.7		1.3		(5.3)		3.1
Total	$	37.2	$	9.0	$	1.3	$	(6.4)	$	41.1

	December 31, 2018		Unrealized Gains (Losses)		Realized Gains		Purchases, Sales, and Settlements, net		December 31, 2019
	(In millions)
Equity securities:
Domestic equity securities	$	4.9	$	(0.3)	$	0.3	$	(0.7)	$	4.2
International equity securities	0.1		(0.1)		—		—		—
Corporate debt securities	21.5		(0.1)		0.1		6.1		27.6
Private assets	1.3		0.2		0.1		3.8		5.4
Total	$	27.8	$	(0.3)	$	0.5	$	9.2	$	37.2

Schedule of Estimated Future Benefit Payments

The following table presents estimated future benefit payments:  

	Pension Benefit Payments		Medical and Life Insurance Benefits
Year Ending December 31,			Gross Benefit Payments		Medicare D Subsidy		Net Benefit Payments
	(In millions)
2021	$	106.9	$	3.5	$	0.1	$	3.4
2022	103.8		3.1		0.1		3.0
2023	100.6		2.8		0.1		2.7
2024	97.1		2.5		0.1		2.4
2025	93.4		2.2		0.1		2.1
Years 2026 - 2030	409.1		7.6		0.2		7.4