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Fair Value Measurements Fair Value Measurements - Reconciliation of Level 3 Assets and Liabilities (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2020 | Dec. 31, 2019
Commercial mortgage loans |  |
Fair Value, Assets Measured on Recurring Basis, Calculation [Roll Forward] |  |
Balance at the beginning of the year | $ 156.6 |
Balance at the end of the year | 163.6 | $ 156.6
Middle market loans |  |
Fair Value, Assets Measured on Recurring Basis, Calculation [Roll Forward] |  |
Balance at the beginning of the year | 111.7 |
Balance at the end of the year | 112.1 | 111.7
Equity securities |  |
Fair Value, Assets Measured on Recurring Basis, Calculation [Roll Forward] |  |
Balance at the beginning of the year | 2.7 |
Balance at the end of the year | 5.0 | 2.7
Recurring | Level 3 |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |
Change in unrealized investment gains (losses) | (5.2) | 0.3
Fair Value, Assets Measured on Recurring Basis, Calculation [Roll Forward] |  |
Balance at the beginning of the year | 279.5 |
Balance at the end of the year | 299.3 | 279.5
Balance at the beginning of the period | 0.0 | 4.6
Balance at the end of the period |  | 0.0
Recurring | Commercial mortgage loans | Level 3 |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |
Change in unrealized investment gains (losses) | 0.1 | 0.3
Fair Value, Assets Measured on Recurring Basis, Calculation [Roll Forward] |  |
Balance at the beginning of the year | 156.4 |
Balance at the end of the year | 163.6 | 156.4
Recurring | Middle market loans | Level 3 |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |
Change in unrealized investment gains (losses) | (5.3) | 0.0
Fair Value, Assets Measured on Recurring Basis, Calculation [Roll Forward] |  |
Balance at the beginning of the year | 111.7 |
Balance at the end of the year | 112.1 | 111.7
Recurring | Asset-backed | Level 3 |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |
Change in unrealized investment gains (losses) | 0.0 | 0.0
Fair Value, Assets Measured on Recurring Basis, Calculation [Roll Forward] |  |
Balance at the beginning of the year | 8.7 |
Balance at the end of the year | 18.6 | 8.7
Recurring | Equity securities | Level 3 |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |
Change in unrealized investment gains (losses) | 0.0 | 0.0
Fair Value, Assets Measured on Recurring Basis, Calculation [Roll Forward] |  |
Balance at the beginning of the year | 2.7 |
Balance at the end of the year | 5.0 | 2.7
Assets | Recurring | Level 3 |  |
Fair Value, Assets Measured on Recurring Basis, Calculation [Roll Forward] |  |
Balance at the beginning of the year | 279.5 | 0.0
Purchases and issuances | 93.0 | 301.5
Settlements and sales | (64.3) | (23.9)
Increase (decrease) in fair value included in net income | (17.2) | 1.8
Balance at the end of the year |  | 279.5
Transfers in/(out) | 8.3 | 0.0
Assets | Recurring | Commercial mortgage loans | Level 3 |  |
Fair Value, Assets Measured on Recurring Basis, Calculation [Roll Forward] |  |
Balance at the beginning of the year | 156.4 | 0.0
Purchases and issuances | 79.7 | 174.7
Settlements and sales | (59.4) | (20.1)
Increase (decrease) in fair value included in net income | (13.1) | 1.7
Balance at the end of the year |  | 156.4
Transfers in/(out) | 0.0 | 0.0
Assets | Recurring | Middle market loans | Level 3 |  |
Fair Value, Assets Measured on Recurring Basis, Calculation [Roll Forward] |  |
Balance at the beginning of the year | 111.7 | 0.0
Purchases and issuances | 0.9 | 115.5
Settlements and sales | (4.8) | (3.8)
Increase (decrease) in fair value included in net income | (4.0) | 0.1
Balance at the end of the year |  | 111.7
Transfers in/(out) | 8.3 | 0.0
Assets | Recurring | Asset-backed | Level 3 |  |
Fair Value, Assets Measured on Recurring Basis, Calculation [Roll Forward] |  |
Balance at the beginning of the year | 8.7 | 0.0
Purchases and issuances | 10.0 | 8.7
Settlements and sales | 0.0 | 0.0
Increase (decrease) in fair value included in net income | (0.1) | 0.0
Balance at the end of the year |  | 8.7
Transfers in/(out) | 0.0 | 0.0
Assets | Recurring | Equity securities | Level 3 |  |
Fair Value, Assets Measured on Recurring Basis, Calculation [Roll Forward] |  |
Balance at the beginning of the year | 2.7 | 0.0
Purchases and issuances | 2.4 | 2.7
Settlements and sales | (0.1) | 0.0
Increase (decrease) in fair value included in net income | 0.0 | 0.0
Balance at the end of the year |  | 2.7
Transfers in/(out) | 0.0 | 0.0
Liability | Recurring | Level 3 |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |
Change in unrealized investment gains (losses), liability | 0.0 | 0.0
Fair Value, Assets Measured on Recurring Basis, Calculation [Roll Forward] |  |
Balance at the beginning of the period | 0.0 |
Liability purchases | 0.0 | 0.0
Liability sales | 0.0 | (7.7)
Liability, increase (decrease) in fv included in net income | 0.0 | 3.1
Balance at the end of the period | 0.0 | 0.0
Liability transfers | 0.0 | 0.0
Liability | Silverton | Recurring | Level 3 |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |
Change in unrealized investment gains (losses), liability | 0.0 |
Fair Value, Assets Measured on Recurring Basis, Calculation [Roll Forward] |  |
Balance at the beginning of the period | 0.0 | 4.6
Liability purchases | 0.0 | 0.0
Liability sales | 0.0 | (7.7)
Liability, increase (decrease) in fv included in net income | 0.0 | 3.1
Balance at the end of the period | 0.0 | 0.0
Liability transfers | $ 0.0 | $ 0.0

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- Definition Amount of unrealized gain (loss) recognized in income from asset measured at fair value on recurring basis using unobservable input (level 3) and still held. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (d) -URI http://asc.fasb.org/extlink&oid=117815213&loc=d3e19207-110258 + Details
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