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Employee Benefits - Changes in the Fair Value of Plan Assets Categorized as Level 3 (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2019 | Dec. 31, 2018
Pension Plan |  |
Reconciliation of changes in the fair value of pension plan assets |  |
Beginning balance at January 1 | $ 2,690.8 | $ 2,966.8
Realized and unrealized gains (losses) | 494.1 | (122.2)
Ending balance at December 31 | 3,007.0 | 2,690.8
Pension Plan | Level 3 |  |
Reconciliation of changes in the fair value of pension plan assets |  |
Beginning balance at January 1 | 0.0 |
Ending balance at December 31 | 0.0 | 0.0
Pension Plan | Level 3 | Private Equity and Real Estate |  |
Reconciliation of changes in the fair value of pension plan assets |  |
Beginning balance at January 1 | 0.0 | 100.1
Realized and unrealized gains (losses) |  | 8.0
Purchases |  | 18.3
Liquidations |  | (1.7)
Transfers out of level 3 |  | (124.7)
Ending balance at December 31 |  | 0.0
Pension Plan | Level 3 | International equity |  |
Reconciliation of changes in the fair value of pension plan assets |  |
Beginning balance at January 1 | 0.0 | 0.8
Realized and unrealized gains (losses) |  | (0.1)
Purchases |  | 0.0
Liquidations |  | 0.0
Transfers out of level 3 |  | (0.7)
Ending balance at December 31 | 0.0 | 0.0
OPEB Plan |  |
Reconciliation of changes in the fair value of pension plan assets |  |
Beginning balance at January 1 | 771.7 | 841.5
Realized and unrealized gains (losses) | 134.3 | (35.2)
Ending balance at December 31 | 879.6 | 771.7
OPEB Plan | Level 3 |  |
Reconciliation of changes in the fair value of pension plan assets |  |
Beginning balance at January 1 | 0.0 |
Ending balance at December 31 | 0.0 | 0.0
OPEB Plan | Level 3 | Private Equity and Real Estate |  |
Reconciliation of changes in the fair value of pension plan assets |  |
Beginning balance at January 1 | 0.0 | 7.7
Realized and unrealized gains (losses) |  | 1.1
Purchases |  | 1.5
Liquidations |  | (0.2)
Transfers out of level 3 |  | (10.1)
Ending balance at December 31 |  | 0.0
OPEB Plan | Level 3 | International equity |  |
Reconciliation of changes in the fair value of pension plan assets |  |
Beginning balance at January 1 | 0.0 | 0.2
Realized and unrealized gains (losses) |  | 0.0
Purchases |  | 0.0
Liquidations |  | 0.0
Transfers out of level 3 |  | (0.2)
Ending balance at December 31 | $ 0.0 | $ 0.0

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- Definition Amount of increase (decrease) in plan assets of defined benefit plan from actual return (loss) determined by change in fair value of plan assets adjusted for contributions, benefit payments, and other expenses. + 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 (b)(1) -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 55 -Paragraph 17 -URI http://asc.fasb.org/extlink&oid=118257860&loc=d3e4179-114921 + 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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- Definition Amount, measured using unobservable input, of decrease in plan asset of defined benefit plan from settlement of trade associated with underlying investment. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (d)(iv)(02)(B) -URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920 + Details
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- Definition Amount, measured using unobservable input, of increase in plan asset of defined benefit plan from purchase. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (d)(iv)(02)(B) -URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920 + Details
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- Definition Amount, measured using unobservable inputs, of increase (decrease) in plan assets of defined benefit plan, for assets transferred into (out of) Level 3 of fair value hierarchy. Includes, but is not limited to, transfer due to change in observability of significant inputs. + 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)(02)(C) -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 55 -Paragraph 17 -URI http://asc.fasb.org/extlink&oid=118257860&loc=d3e4179-114921 + Details
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