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Employee Benefits - Plan Assets and Investment Policy (Details) - USD ($) $ in Millions | Dec. 31, 2019 | Dec. 31, 2018
--- | --- | ---
Employee Benefits |  |
Weighted-average asset allocations (as a percent) | 100.00% | 100.00%
Fair value of plan assets | $ 104.7 | $ 92.2
Investments measured at net asset value (NAV) | 2.4 | 2.7
Total investments at fair value | 107.1 | 94.9
Level 1 |  |
Employee Benefits |  |
Fair value of plan assets | 91.8 | 63.3
Total investments at fair value | 91.8 | 63.3
Level 2 |  |
Employee Benefits |  |
Fair value of plan assets | 12.9 | 28.9
Total investments at fair value | 12.9 | 28.9
Equity securities |  |
Employee Benefits |  |
Fair value of plan assets | 25.1 | 27.5
Equity securities | Level 1 |  |
Employee Benefits |  |
Fair value of plan assets | 25.1 | 27.5
U.S. government, state, and agency |  |
Employee Benefits |  |
Fair value of plan assets | 9.3 | 11.6
U.S. government, state, and agency | Level 2 |  |
Employee Benefits |  |
Fair value of plan assets | 9.3 | 11.6
Corporate debt securities |  |
Employee Benefits |  |
Fair value of plan assets | 3.6 | 17.3
Corporate debt securities | Level 2 |  |
Employee Benefits |  |
Fair value of plan assets | 3.6 | 17.3
Mutual funds |  |
Employee Benefits |  |
Fair value of plan assets | 59.4 | 32.2
Mutual funds | Level 1 |  |
Employee Benefits |  |
Fair value of plan assets | 59.4 | 32.2
Cash and cash equivalents |  |
Employee Benefits |  |
Fair value of plan assets | 7.3 | 3.6
Cash and cash equivalents | Level 1 |  |
Employee Benefits |  |
Fair value of plan assets | $ 7.3 | $ 3.6
Equity securities |  |
Employee Benefits |  |
Weighted-average asset allocations (as a percent) | 33.00% | 51.00%
Debt securities |  |
Employee Benefits |  |
Weighted-average asset allocations (as a percent) | 60.00% | 45.00%
Cash and cash equivalents |  |
Employee Benefits |  |
Weighted-average asset allocations (as a percent) | 7.00% | 4.00%

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- Definition Amount of asset segregated and restricted to provide benefit under defined benefit plan. Asset includes, but is not limited to, stock, bond, other investment, earning from investment, and contribution by employer and employee excluding NAV valuation. + References No definition available. + Details
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- Definition Amount of asset segregated and restricted to provide benefit under defined benefit plan. Asset includes, but is not limited to, stock, bond, other investment, earning from investment, and contribution by employer and employee. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (d)(iv)(01) -URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920 Reference 2: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (d)(iv)(01) -URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (d)(ii) -URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920 Reference 4: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 55 -Paragraph 17 -URI http://asc.fasb.org/extlink&oid=118257860&loc=d3e4179-114921 Reference 5: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920 Reference 6: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (d)(ii) -URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920 + Details
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