Pensions and Other Postretirement Plans (Narrative) (Details)	1 Months Ended	2 Months Ended	3 Months Ended			10 Months Ended	12 Months Ended
	Dec. 31, 2019 USD ($) retirees_beneficiaries Investment companies	Dec. 31, 2018 USD ($) Investment	Dec. 31, 2018 USD ($) Investment	Dec. 31, 2017 USD ($)	Sep. 30, 2017 USD ($)	Oct. 31, 2018	Dec. 31, 2019 USD ($) multiemployer_plan Investment companies	Dec. 31, 2018 USD ($) multiemployer_plan Investment	Dec. 31, 2017 USD ($) multiemployer_plan
Retirement Benefits Disclosure [Line Items]
Expense associated with the retirement benefits provided under incentive savings plans							$ 9,800,000	$ 8,600,000	$ 7,500,000
Multiemployer Pension Plans [Member]
Retirement Benefits Disclosure [Line Items]
Number of multiemployer plans contributed to | multiemployer_plan							1	1	1
Contributions to multiemployer pension plans							$ 100,000	$ 100,000	$ 100,000
Pension Plans [Member]
Retirement Benefits Disclosure [Line Items]
Settlement of obligation							235,544,000	95,777,000
Settlement			$ 26,900,000				91,676,000	26,917,000	0
Early retirement and special separation benefit program expense							6,432,000	0	1,825,000
Accumulated benefit obligation	$ 991,100,000	$ 1,097,300,000	$ 1,097,300,000				991,100,000	1,097,300,000
Company contributions							0	0
Estimated employer contributions in next fiscal year	$ 0						0
Net Periodic Cost (Benefit) for the Year							(52,665,000)	(74,031,000)	(59,039,000)
Curtailment							$ 0	$ 806,000	0
Percent of Plan Assets Managed Internally by Company							39.00%
Percent Of Plan Assets Managed By Investment Companies							61.00%
Number of investment companies actively managing plan assets | companies	2						2
Percentage of total plan assets	100.00%	100.00%	100.00%				100.00%	100.00%
Pension Plans [Member] | Irrevocable Group Annuity Contract Purchase [Member]
Retirement Benefits Disclosure [Line Items]
Payment for settlement	$ 216,800,000
Settlement of obligation	$ 212,100,000
Number of retirees and beneficiaries | retirees_beneficiaries	3,800
Settlement	$ 91,700,000
Supplemental Executive Retirement Plan (SERP) [Member]
Retirement Benefits Disclosure [Line Items]
Accumulated benefit obligation	$ 114,800,000	$ 102,200,000	$ 102,200,000				$ 114,800,000	$ 102,200,000
Company contributions							7,071,000	5,694,000
Other Postretirement Plans [Member]
Retirement Benefits Disclosure [Line Items]
Company contributions							750,000	782,000
Net Periodic Cost (Benefit) for the Year							(11,434,000)	(3,679,000)	(2,232,000)
Curtailment							$ 0	$ 3,380,000	$ 0
Discount rate to determine benefit obligation	2.68%	3.69%	3.69%				2.68%	3.69%
Discount rate to determine periodic cost		4.04%				3.11%	3.69%		3.31%
Other Postretirement Plans [Member] | Pre-Age 65 [Member]
Retirement Benefits Disclosure [Line Items]
Assumed health care cost trend rate	7.00%						7.00%
Direction of change for assumed health care cost trend rate							decreasing
Ultimate health care cost trend rate	4.50%						4.50%
Year that rate reaches ultimate trend rate							2026
Other Postretirement Plans [Member] | Post-Age 65 [Member]
Retirement Benefits Disclosure [Line Items]
Assumed health care cost trend rate	7.49%						7.49%
Direction of change for assumed health care cost trend rate							decreasing
Ultimate health care cost trend rate	4.50%						4.50%
Year that rate reaches ultimate trend rate							2026
Other Postretirement Plans [Member] | Medicare Advantage [Member]
Retirement Benefits Disclosure [Line Items]
Assumed health care cost trend rate	(6.89%)						(6.89%)
Assumed health care cost trend rate, 2021	8.15%						8.15%
Direction of change for assumed health care cost trend rate							decreasing
Ultimate health care cost trend rate	4.50%						4.50%
Year that rate reaches ultimate trend rate							2029
Single Equity Concentration [Member] | Pension Plans [Member]
Retirement Benefits Disclosure [Line Items]
Defined benefit plan, target allocation maximum percentage of assets, singular equity security, without prior approval by plan administrator							10.00%
Value of investments	$ 704,800,000	$ 945,600,000	$ 945,600,000				$ 704,800,000	$ 945,600,000
Percentage of total plan assets	30.00%	45.00%	45.00%				30.00%	45.00%
Single Equity Concentration [Member] | Equity securities [Member] | Pension Plans [Member]
Retirement Benefits Disclosure [Line Items]
Number of investments the company's pension plan held which individually exceed 10% of total plan assets | Investment	1	1	1				1	1
Single Equity Concentration [Member] | Equity funds [Member] | Pension Plans [Member]
Retirement Benefits Disclosure [Line Items]
Number of investments the company's pension plan held which individually exceed 10% of total plan assets | Investment	1	1	1				1	1
Defined Benefit Plan Assets Total [Member] | Concentration In Single Entity, Type Of Industry, Foreign Country Or Individual Fund [Member] | Pension Plans [Member]
Retirement Benefits Disclosure [Line Items]
Minimum percentage of plan assets considered as significant concentrations in pension plans							10.00%
Separation Incentive Program [Member] | Pension Plans [Member] | Forney [Member]
Retirement Benefits Disclosure [Line Items]
Early retirement and special separation benefit program expense					$ 900,000
Education [Member] | Separation Incentive Program [Member] | Pension Plans [Member]
Retirement Benefits Disclosure [Line Items]
Early retirement and special separation benefit program expense				$ 900,000			$ 6,400,000
Investment Manager 1 [Member] | Alphabet And Berkshire Hathaway Common Stock [Member] | Pension Plans [Member]
Retirement Benefits Disclosure [Line Items]
Defined benefit plan, target allocation maximum percentage of assets, singular equity security, without prior approval by plan administrator							15.00%
Investment Manager 1 [Member] | Maximum [Member] | Foreign Investments [Member] | Pension Plans [Member]
Retirement Benefits Disclosure [Line Items]
Defined benefit plan, target allocation percentage of assets	30.00%						30.00%
Investment Manager 1 [Member] | Minimum [Member] | Fixed income securities [Member] | Pension Plans [Member]
Retirement Benefits Disclosure [Line Items]
Defined benefit plan, target allocation percentage of assets	5.00%						5.00%
Investment Manager 2 [Member] | Berkshire Hathaway Common Stock [Member] | Pension Plans [Member]
Retirement Benefits Disclosure [Line Items]
Defined benefit plan, target allocation maximum percentage of assets, singular equity security, without prior approval by plan administrator							20.00%
Investment Manager 2 [Member] | Maximum [Member] | Foreign Investments [Member] | Pension Plans [Member]
Retirement Benefits Disclosure [Line Items]
Defined benefit plan, target allocation percentage of assets	15.00%						15.00%
Investment Manager 2 [Member] | Minimum [Member] | Fixed income securities [Member] | Pension Plans [Member]
Retirement Benefits Disclosure [Line Items]
Defined benefit plan, target allocation percentage of assets	10.00%						10.00%