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Mortgage Servicing Rights, Net - Additional Information (Detail) - USD ($) $ in Millions | 3 Months Ended | 12 Months Ended
--- | --- | ---
Mar. 31, 2021 | Dec. 31, 2020
Mortgage Servicing Rights |  |
Primary servicing portfolio | $ 67,900.0 | $ 66,300.0
Special servicing portfolio | 2,200.0 | 2,300.0
Discount Rate One |  |
Mortgage Servicing Rights |  |
Decrease in fair value of servicing rights | 16.3 | 14.8
Discount Rate Two |  |
Mortgage Servicing Rights |  |
Decrease in fair value of servicing rights | $ 31.8 | $ 28.9
Minimum |  |
Mortgage Servicing Rights |  |
Discount rates used in measuring fair value (in percentage) | 6.10% | 6.10%
Minimum | Discount Rate One |  |
Mortgage Servicing Rights |  |
Increase in discount rate (in percentage) | 1.00% |
Maximum |  |
Mortgage Servicing Rights |  |
Discount rates used in measuring fair value (in percentage) | 13.50% | 13.50%
Maximum | Discount Rate Two |  |
Mortgage Servicing Rights |  |
Increase in discount rate (in percentage) | 2.00% |
Mortgage Servicing Rights |  |
Mortgage Servicing Rights |  |
Estimated fair value of MSRs | $ 570.4 | $ 527.1

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- Definition Fair value of an asset representing net future revenue from contractually specified servicing fees, late charges, and other ancillary revenues, in excess of future costs related to servicing arrangements. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 860 -SubTopic 50 -Section 45 -Paragraph 2 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=6469459&loc=d3e122501-111745 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 860 -SubTopic 50 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6469459&loc=d3e122492-111745 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 860 -SubTopic 50 -Section 50 -Paragraph 3 -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=116651436&loc=d3e122625-111746 Reference 4: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 860 -SubTopic 50 -Section 45 -Paragraph 2 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=6469459&loc=d3e122501-111745 + Details
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