Operating Segments and Related Disclosures - Selected Financial Information for Each Reportable Segment (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Net Sales:
Net favorable effect of the changes in contract estimates on net sales	$ 2,188.0	$ 2,072.7	$ 1,981.5
Segment Performance:
Environmental remediation provision adjustments	(4.1)	(4.3)	(2.1)
Retirement benefits, net	(38.0)
Reconciliation of segment performance to income before income taxes:
Interest expense	(20.1)	(30.1)	(35.7)
Interest income	2.5	6.3	15.5
Stock-based compensation	(20.7)	(31.4)	(27.3)
Income before income taxes	195.0	180.2	191.9
Capital Expenditures	37.3	54.6	43.9
Depreciation and amortization	61.4	65.3	74.5
Aerospace and Defense
Reconciliation of segment performance to income before income taxes:
Capital Expenditures	37.3	54.6	42.9
Depreciation and amortization	60.5	64.2	72.9
Real Estate Segment
Reconciliation of segment performance to income before income taxes:
Capital Expenditures	0.0	0.0	0.0
Depreciation and amortization	0.7	0.8	1.2
Operating Segments
Net Sales:
Net favorable effect of the changes in contract estimates on net sales	2,188.0	2,072.7	1,981.5
Segment Performance:
Segment performance	288.8	273.8	271.4
Reconciliation of segment performance to income before income taxes:
Segment performance	288.8	273.8	271.4
Operating Segments | Aerospace and Defense
Net Sales:
Net favorable effect of the changes in contract estimates on net sales	2,179.3	2,069.4	1,974.0
Segment Performance:
Aerospace and Defense	282.3	264.2	249.1
Environmental remediation provision adjustments	(3.8)	(2.7)	(1.9)
Retirement benefits, net	11.5	14.7	22.4
Unusual items	(4.1)	(0.6)	(0.3)
Segment performance	285.9	275.6	269.3
Reconciliation of segment performance to income before income taxes:
Segment performance	285.9	275.6	269.3
Unusual items	(4.1)	(0.6)	(0.3)
Operating Segments | Real Estate Segment
Net Sales:
Net favorable effect of the changes in contract estimates on net sales	8.7	3.3	7.5
Segment Performance:
Segment performance	2.9	(1.8)	2.1
Reconciliation of segment performance to income before income taxes:
Segment performance	2.9	(1.8)	2.1
Segment Reconciling Items
Segment Performance:
Unusual items	(25.3)	(7.5)	0.0
Reconciliation of segment performance to income before income taxes:
Interest expense	(20.1)	(30.1)	(35.7)
Interest income	2.5	6.3	15.5
Stock-based compensation	(20.7)	(31.4)	(27.3)
Unusual items	(25.3)	(7.5)	0.0
Corporate
Segment Performance:
Retirement benefits, net	(6.6)	(7.5)	(7.2)
Reconciliation of segment performance to income before income taxes:
Corporate and other	(23.6)	(23.4)	(24.8)
Capital Expenditures	0.0	0.0	1.0
Depreciation and amortization	$ 0.2	$ 0.3	$ 0.4