11. GOODWILL AND INTANGIBLE ASSETS, NET The following table presents the details of goodwill by segment (in millions): | | | | | | | | | | | | | | | | | | | | | | | | North American | | European | | | | | Corporate | | | | | | | Options | | Equities | | Equities | | Global FX | | and Other | | Total | | Balance as of December 31, 2018 | | $ | 239.4 | | $ | 1,740.4 | | $ | 425.6 | | $ | 267.2 | | $ | 18.8 | | $ | 2,691.4 | | Dispositions | | | — | | | — | | | — | | | — | | | (8.3) | | | (8.3) | | Impairment | | | — | | | — | | | — | | | — | | | (10.5) | | | (10.5) | | Changes in foreign currency exchange rates | | | — | | | — | | | 9.5 | | | — | | | — | | | 9.5 | | Balance as of December 31, 2019 | | $ | 239.4 | | $ | 1,740.4 | | $ | 435.1 | | $ | 267.2 | | $ | — | | $ | 2,682.1 | | Additions | | | 66.4 | | | 134.8 | | | — | | | — | | | — | | | 201.2 | | Changes in foreign currency exchange rates | | | — | | | 2.1 | | | 9.7 | | | — | | | — | | | 11.8 | | Balance as of December 31, 2020 | | $ | 305.8 | | $ | 1,877.3 | | $ | 444.8 | | $ | 267.2 | | $ | — | | $ | 2,895.1 | |
Goodwill has been allocated to specific reporting units for purposes of impairment testing - Options, North American Equities, European Equities and Global FX. No goodwill has been allocated to Futures. Goodwill impairment testing is performed annually in the fiscal fourth quarter or more frequently if conditions exist that indicate that the asset may be impaired. The following table presents the details of the intangible assets (in millions): | | | | | | | | | | | | | | | | | | | | | | | | North American | | European | | | | | Corporate | | | | | | | Options | | Equities | | Equities | | Global FX | | and Other | | Total | | Balance as of December 31, 2018 | | $ | 181.9 | | $ | 990.3 | | $ | 376.9 | | $ | 166.9 | | $ | 4.2 | | $ | 1,720.2 | | Additions | | | — | | | — | | | — | | | — | | | — | | | — | | Dispositions | | | — | | | — | | | — | | | — | | | (3.3) | | | (3.3) | | Amortization | | | (15.3) | | | (68.9) | | | (24.8) | | | (28.7) | | | (0.9) | | | (138.6) | | Changes in foreign currency exchange rates | | | — | | | — | | | 11.6 | | | — | | | — | | | 11.6 | | Balance as of December 31, 2019 | | $ | 166.6 | | $ | 921.4 | | $ | 363.7 | | $ | 138.2 | | $ | — | | $ | 1,589.9 | | Additions | | | 22.3 | | | 193.1 | | | 32.3 | | | — | | | — | | | 247.7 | | Amortization | | | (15.5) | | | (61.0) | | | (23.4) | | | (24.9) | | | — | | | (124.8) | | Changes in foreign currency exchange rates | | | — | | | 2.0 | | | 14.2 | | | — | | | — | | | 16.2 | | Balance as of December 31, 2020 | | $ | 173.4 | | $ | 1,055.5 | | $ | 386.8 | | $ | 113.3 | | $ | — | | $ | 1,729.0 | |
For the years ended December 31, 2020, 2019 and 2018, amortization expense was $124.8 million, $138.6 million and $160.0 million, respectively. The estimated future amortization expense is $123.7 million for 2021, $110.7 million for 2022, $99.4 million for 2023, $77.8 million for 2024, and $67.2 million for 2025. The following tables present the categories of intangible assets at December 31, 2020 and 2019 (in millions): | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Weighted | | | December 31, 2020 | | Average | | | | | North American | | European | | | | | Amortization | | | Options | | Equities | | Equities | | Global FX | | Period (in years) | Trading registrations and licenses | | $ | 95.5 | | $ | 592.0 | | $ | 219.3 | | $ | — | | Indefinite | Customer relationships | | | 46.6 | | | 378.3 | | | 175.7 | | | 140.0 | | 16 | Market data customer relationships | | | 53.6 | | | 322.0 | | | 65.9 | | | 64.4 | | 11 | Technology | | | 28.1 | | | 41.1 | | | 28.6 | | | 22.5 | | 5 | Trademarks and tradenames | | | 12.9 | | | 7.8 | | | 2.6 | | | 1.2 | | 9 | Accumulated amortization | | | (63.3) | | | (285.7) | | | (105.3) | | | (114.8) | | | | | $ | 173.4 | | $ | 1,055.5 | | $ | 386.8 | | $ | 113.3 | | |
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | Weighted | | | December 31, 2019 | | Average | | | | | North American | | European | | | | | Amortization | | | Options | | Equities | | Equities | | Global FX | | Period (in years) | Trading registrations and licenses | | $ | 95.5 | | $ | 572.7 | | $ | 182.2 | | $ | — | | Indefinite | Customer relationships | | | 38.8 | | | 222.9 | | | 169.7 | | | 140.0 | | 17 | Market data customer relationships | | | 53.6 | | | 322.0 | | | 63.6 | | | 64.4 | | 12 | Technology | | | 24.8 | | | 22.5 | | | 23.9 | | | 22.5 | | 4 | Trademarks and tradenames | | | 1.7 | | | 6.0 | | | 1.9 | | | 1.2 | | 6 | Accumulated amortization | | | (47.8) | | | (224.7) | | | (77.6) | | | (89.9) | | | | | $ | 166.6 | | $ | 921.4 | | $ | 363.7 | | $ | 138.2 | | |
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