The following tables present gross unrealized losses and fair value for those available-for-sale debt securities that were in an unrealized loss position as of June 30, 2022 and December 31, 2021, aggregated by investment category and length of time that the individual securities have been in a continuous loss position (in millions):
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Less than 12 months | | 12 months or longer | | Total | As of June 30, 2022 | Fair Value | | Gross Unrealized Losses | | Fair Value | | Gross Unrealized Losses | | Fair Value | | Gross Unrealized Losses | U.S. government and agency securities | $ | 2,251.7 | | | $ | (48.2) | | | $ | 44.7 | | | $ | (1.3) | | | $ | 2,296.4 | | | $ | (49.5) | | Corporate debt securities | 509.4 | | | (14.0) | | | 8.3 | | | (0.4) | | | 517.7 | | | (14.4) | | Total | $ | 2,761.1 | | | $ | (62.2) | | | $ | 53.0 | | | $ | (1.7) | | | $ | 2,814.1 | | | $ | (63.9) | |
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Less than 12 months | | 12 months or longer | | Total | As of December 31, 2021 | Fair Value | | Gross Unrealized Losses | | Fair Value | | Gross Unrealized Losses | | Fair Value | | Gross Unrealized Losses | U.S. government and agency securities | $ | 1,729.9 | | | $ | (7.3) | | | $ | — | | | $ | — | | | $ | 1,729.9 | | | $ | (7.3) | | Corporate debt securities | 352.3 | | | (2.0) | | | — | | | — | | | 352.3 | | | (2.0) | | Total | $ | 2,082.2 | | | $ | (9.3) | | | $ | — | | | $ | — | | | $ | 2,082.2 | | | $ | (9.3) | |
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