Financial Information for Subsidiary and Guarantor Parent (B.S.) (Details) - USD ($) $ in Millions	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Jun. 30, 2018	Mar. 31, 2018	Jan. 01, 2018	Dec. 31, 2017
ASSETS
Cash and cash equivalents	$ 281.2		$ 382.0	$ 122.4			$ 141.6
Accounts receivable, net	581.4		527.8
Intercompany notes receivable	0.0		0.0
Short-term contract assets	40.9		51.2	47.7		$ 36.5
Inventories, net	1,217.5		1,211.1
Prepaid expenses and other current assets	140.4		74.6
Total current assets	2,261.4		2,246.7
Property, plant and equipment, net	2,404.9		2,475.0
Goodwill	524.8		534.7
Intercompany notes receivable	0.0		0.0
Long-term contract assets	0.1		0.1	0.1		16.9
Investment in subsidiaries	0.0		0.0
Other assets	358.2		245.4
Total assets	5,549.3		5,501.8
LIABILITIES AND EQUITY
Accounts payable	420.6		498.8
Intercompany notes payable	0.0		0.0
Short-term contract liabilities	69.3		71.4	70.4		69.7
Short-term debt and current portion of long-term debt	11.5		6.6
Other current liabilities	257.8		260.1
Total current liabilities	759.2		836.9
Long-term debt	1,537.1		1,535.5
Intercompany notes payable	0.0		0.0
Accrued postretirement benefits	305.4		318.4
Pension liabilities	669.6		730.0
Deferred income taxes	15.1		12.9
Long-term contract liabilities	7.3		7.3	14.6		$ 22.2
Other long-term liabilities	124.3		76.5
Total liabilities	3,410.7		3,510.2
Total stockholders’ equity	2,138.6	$ 2,046.6	1,991.6	$ 2,041.9	$ 1,963.3		$ 1,844.5
Total Liabilities and Equity	5,549.3		5,501.8
Reportable Legal Entities | Parent Company
ASSETS
Cash and cash equivalents	7.4		0.1
Accounts receivable, net	0.0		0.0
Intercompany notes receivable	0.0		0.0
Short-term contract assets	0.0		0.0
Inventories, net	0.0		0.0
Prepaid expenses and other current assets	6.5		12.9
Total current assets	13.9		13.0
Property, plant and equipment, net	3.1		1.7
Goodwill	0.0		0.0
Intercompany notes receivable	0.0		0.0
Investment in subsidiaries	6,367.3		6,096.4
Other assets	55.0		35.6
Total assets	6,439.3		6,146.7
LIABILITIES AND EQUITY
Accounts payable	6.0		3.3
Intercompany notes payable	2,300.7		2,102.8
Short-term contract liabilities	0.0		0.0
Short-term debt and current portion of long-term debt	0.5		0.2
Other current liabilities	53.6		59.1
Total current liabilities	2,360.8		2,165.4
Long-term debt	1,281.1		1,278.8
Intercompany notes payable	0.0		0.0
Accrued postretirement benefits	0.0		0.0
Pension liabilities	622.5		681.6
Deferred income taxes	15.1		12.9
Other long-term liabilities	21.2		16.4
Total liabilities	4,300.7		4,155.1
Total stockholders’ equity	2,138.6		1,991.6
Total Liabilities and Equity	6,439.3		6,146.7
Reportable Legal Entities | Subsidiary
ASSETS
Cash and cash equivalents	7.7		10.8
Accounts receivable, net	151.6		126.3
Intercompany notes receivable	0.0		0.0
Short-term contract assets	0.0		0.0
Inventories, net	265.2		216.1
Prepaid expenses and other current assets	60.7		29.3
Total current assets	485.2		382.5
Property, plant and equipment, net	1,533.4		1,548.4
Goodwill	0.0		0.0
Intercompany notes receivable	0.0		0.0
Investment in subsidiaries	37.7		37.7
Other assets	55.2		30.7
Total assets	2,111.5		1,999.3
LIABILITIES AND EQUITY
Accounts payable	154.2		177.5
Intercompany notes payable	2,029.5		1,866.0
Short-term contract liabilities	48.0		33.0
Short-term debt and current portion of long-term debt	0.0		0.7
Other current liabilities	71.6		71.7
Total current liabilities	2,303.3		2,148.9
Long-term debt	149.7		151.8
Intercompany notes payable	200.0		200.0
Accrued postretirement benefits	254.8		259.2
Pension liabilities	3.7		4.0
Deferred income taxes	0.0		0.0
Other long-term liabilities	35.8		17.6
Total liabilities	2,947.3		2,781.5
Total stockholders’ equity	(835.8)		(782.2)
Total Liabilities and Equity	2,111.5		1,999.3
Reportable Legal Entities | NonGuarantor Subsidiaries
ASSETS
Cash and cash equivalents	266.1		371.1
Accounts receivable, net	429.8		401.5
Intercompany notes receivable	4,330.2		3,968.8
Short-term contract assets	40.9		51.2
Inventories, net	952.3		995.0
Prepaid expenses and other current assets	73.2		32.4
Total current assets	6,092.5		5,820.0
Property, plant and equipment, net	868.4		924.9
Goodwill	524.8		534.7
Intercompany notes receivable	200.0		200.0
Investment in subsidiaries	0.0		0.0
Other assets	248.0		179.1
Total assets	7,933.7		7,658.7
LIABILITIES AND EQUITY
Accounts payable	260.4		318.0
Intercompany notes payable	0.0		0.0
Short-term contract liabilities	21.3		38.4
Short-term debt and current portion of long-term debt	11.0		5.7
Other current liabilities	132.6		129.3
Total current liabilities	425.3		491.4
Long-term debt	106.3		104.9
Intercompany notes payable	0.0		0.0
Accrued postretirement benefits	50.6		59.2
Pension liabilities	43.4		44.4
Deferred income taxes	0.0		0.0
Other long-term liabilities	67.3		42.5
Total liabilities	692.9		742.4
Total stockholders’ equity	7,240.8		6,916.3
Total Liabilities and Equity	7,933.7		7,658.7
Eliminations
ASSETS
Cash and cash equivalents	0.0		0.0
Accounts receivable, net	0.0		0.0
Intercompany notes receivable	(4,330.2)		(3,968.8)
Short-term contract assets	0.0		0.0
Inventories, net	0.0		0.0
Prepaid expenses and other current assets	0.0		0.0
Total current assets	(4,330.2)		(3,968.8)
Property, plant and equipment, net	0.0		0.0
Goodwill	0.0		0.0
Intercompany notes receivable	(200.0)		(200.0)
Investment in subsidiaries	(6,405.0)		(6,134.1)
Other assets	0.0		0.0
Total assets	(10,935.2)		(10,302.9)
LIABILITIES AND EQUITY
Accounts payable	0.0		0.0
Intercompany notes payable	(4,330.2)		(3,968.8)
Short-term contract liabilities	0.0		0.0
Short-term debt and current portion of long-term debt	0.0		0.0
Other current liabilities	0.0		0.0
Total current liabilities	(4,330.2)		(3,968.8)
Long-term debt	0.0		0.0
Intercompany notes payable	(200.0)		(200.0)
Accrued postretirement benefits	0.0		0.0
Pension liabilities	0.0		0.0
Deferred income taxes	0.0		0.0
Other long-term liabilities	0.0		0.0
Total liabilities	(4,530.2)		(4,168.8)
Total stockholders’ equity	(6,405.0)		(6,134.1)
Total Liabilities and Equity	$ (10,935.2)		$ (10,302.9)