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Commitments and Contingencies - Additional Information (Detail) - Environmental Matters $ in Millions | 12 Months Ended
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Dec. 31, 2020 USD ($) facilities | Dec. 31, 2019 USD ($) | Dec. 31, 2018 USD ($)
Contingencies And Commitments [Line Items] |  |  |
Pretax charge to comply U.S. federal, state and local environmental control and protection regulations | $ 16.3 | $ 15.9 | $ 14.7
Capital expenditure to comply environmental regulations | 1.2 | 1.4 | $ 1.7
Environmental reserves | 91.3 | 90.8 |
Environmental reserves included in current liabilities | $ 7.1 | 10.4 |
Nuclear Operations Group |  |  |
Contingencies And Commitments [Line Items] |  |  |
Number of facilities | facilities | 2 |  |
Financial assurance to pay expected cost of decommissioning | $ 61.8 |  |
Nuclear Energy Group |  |  |
Contingencies And Commitments [Line Items] |  |  |
Financial assurance to pay expected cost of decommissioning | $ 47.9 | $ 47.0 |

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- Definition Total costs accrued as of the balance sheet date for environmental loss contingencies. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 450 -SubTopic 20 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=121557415&loc=d3e14326-108349 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 450 -SubTopic 20 -Section 25 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=6395460&loc=d3e13647-108346 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 410 -SubTopic 30 -Section 50 -Paragraph 7 -URI http://asc.fasb.org/extlink&oid=6393242&loc=d3e13207-110859 + Details
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