Adoption of Revenue Recognition - Effect of Revenue Recognition on Condensed Consolidated Balance Sheet (Details) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017	Dec. 31, 2016
Current Assets
Cash and cash equivalents	$ 432.8	$ 535.0	$ 382.1	$ 410.3
Marketable securities	20.0	20.0
Accounts receivable	170.1	64.5
Contract assets	266.0	268.1
Other current assets, net	156.7	129.1
Total Current Assets	1,045.6	1,016.7
Noncurrent Assets
Property, plant and equipment, net	352.8	359.0
Recoverable environmental remediation costs	228.1	231.1
Deferred income taxes	253.1	145.8
Goodwill	161.3	161.3
Intangible assets	82.1	85.5
Other noncurrent assets, net	262.9	259.3
Total Noncurrent Assets	1,340.3	1,242.0
Total Assets	2,385.9	2,258.7
Current Liabilities
Current portion of long-term debt	27.7	25.0
Accounts payable	133.4	100.9
Reserves for environmental remediation costs	36.4	35.2
Contract liabilities	212.6	276.8
Other current liabilities	267.6	156.9
Total Current Liabilities	677.7	594.8
Total Noncurrent Liabilities	1,539.0	1,561.5
Total Liabilities	2,216.7	2,156.3
Stockholders’ Equity
Common stock	7.4	7.4
Other capital	505.8	503.1
Treasury stock at cost	(64.5)	(64.5)
Accumulated deficit	(19.4)	(71.0)
Accumulated other comprehensive loss, net of income taxes	(260.1)	(272.6)
Total Stockholders’ Equity	169.2	102.4
Total Liabilities and Stockholders’ Equity	2,385.9	2,258.7
Effect of Adoption | ASU 2014-09
Current Assets
Cash and cash equivalents	0.0	0.0
Marketable securities	0.0
Accounts receivable	(81.2)
Contract assets	36.1
Other current assets, net	(10.9)
Total Current Assets	(56.0)
Noncurrent Assets
Property, plant and equipment, net	0.0
Recoverable environmental remediation costs	0.0
Deferred income taxes	(118.5)
Goodwill	0.0
Intangible assets	0.0
Other noncurrent assets, net	0.0
Total Noncurrent Assets	(118.5)
Total Assets	(174.5)
Current Liabilities
Current portion of long-term debt	0.0
Accounts payable	0.0
Reserves for environmental remediation costs	0.0
Contract liabilities	0.5
Other current liabilities	(131.5)
Total Current Liabilities	(131.0)
Total Noncurrent Liabilities	0.0
Total Liabilities	(131.0)
Stockholders’ Equity
Common stock	0.0
Other capital	0.0
Treasury stock at cost	0.0
Accumulated deficit	(43.5)
Accumulated other comprehensive loss, net of income taxes	0.0
Total Stockholders’ Equity	(43.5)
Total Liabilities and Stockholders’ Equity	(174.5)
Amounts Excluding Effect of Adoption
Current Assets
Cash and cash equivalents	432.8	$ 535.0
Marketable securities	20.0
Accounts receivable	88.9
Contract assets	302.1
Other current assets, net	145.8
Total Current Assets	989.6
Noncurrent Assets
Property, plant and equipment, net	352.8
Recoverable environmental remediation costs	228.1
Deferred income taxes	134.6
Goodwill	161.3
Intangible assets	82.1
Other noncurrent assets, net	262.9
Total Noncurrent Assets	1,221.8
Total Assets	2,211.4
Current Liabilities
Current portion of long-term debt	27.7
Accounts payable	133.4
Reserves for environmental remediation costs	36.4
Contract liabilities	213.1
Other current liabilities	136.1
Total Current Liabilities	546.7
Total Noncurrent Liabilities	1,539.0
Total Liabilities	2,085.7
Stockholders’ Equity
Common stock	7.4
Other capital	505.8
Treasury stock at cost	(64.5)
Accumulated deficit	(62.9)
Accumulated other comprehensive loss, net of income taxes	(260.1)
Total Stockholders’ Equity	125.7
Total Liabilities and Stockholders’ Equity	$ 2,211.4