Other comprehensive income - Schedule of Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) |
3 Months Ended | 6 Months Ended | |||
|---|---|---|---|---|---|
Jun. 30, 2026 |
Jun. 30, 2025 |
Jun. 30, 2026 |
Jun. 30, 2025 |
Dec. 31, 2025 |
|
| AOCI Attributable to Parent, Net of Tax [Roll Forward] | |||||
| Beginning balance | $ 6,311,086,000 | $ 5,799,695,000 | $ 6,249,079,000 | $ 5,613,066,000 | |
| Total other comprehensive income, net of tax | 9,302,000 | 94,330,000 | 22,701,000 | 265,583,000 | |
| Ending balance | 6,433,005,000 | 5,954,018,000 | 6,433,005,000 | 5,954,018,000 | |
| Accumulated other comprehensive loss, net of tax | (1,159,386,000) | (1,159,386,000) | $ (1,182,087,000) | ||
| Accumulated other comprehensive loss | |||||
| AOCI Attributable to Parent, Net of Tax [Roll Forward] | |||||
| Beginning balance | (1,168,688,000) | (1,489,987,000) | (1,182,087,000) | (1,661,240,000) | |
| Total other comprehensive income, net of tax | 9,302,000 | 94,330,000 | 22,701,000 | 265,583,000 | |
| Ending balance | (1,159,386,000) | (1,395,657,000) | (1,159,386,000) | (1,395,657,000) | |
| Foreign currency translation | |||||
| AOCI Attributable to Parent, Net of Tax [Roll Forward] | |||||
| Beginning balance | (85,538,000) | (78,011,000) | (85,282,000) | (71,365,000) | |
| Other comprehensive (loss) income before reclassifications | 22,428,000 | 7,499,000 | 22,172,000 | 854,000 | |
| Total other comprehensive income, net of tax | 22,428,000 | 7,499,000 | 22,172,000 | 854,000 | |
| Ending balance | (63,110,000) | (70,511,000) | (63,110,000) | (70,511,000) | |
| Adjustment of pension and postretirement benefit plans | |||||
| AOCI Attributable to Parent, Net of Tax [Roll Forward] | |||||
| Beginning balance | (89,744,000) | (93,271,000) | (91,155,000) | (94,692,000) | |
| Amounts reclassified from accumulated other comprehensive loss for amortization of net losses | 1,411,000 | 1,420,000 | 2,822,000 | 2,841,000 | |
| Total other comprehensive income, net of tax | 1,411,000 | 1,420,000 | 2,822,000 | 2,841,000 | |
| Ending balance | (88,333,000) | (91,851,000) | (88,333,000) | (91,851,000) | |
| Unrealized net holding losses on debt securities | |||||
| AOCI Attributable to Parent, Net of Tax [Roll Forward] | |||||
| Beginning balance | (993,406,000) | (1,318,705,000) | (1,005,650,000) | (1,495,183,000) | |
| Other comprehensive (loss) income before reclassifications | (49,647,000) | 48,417,000 | (74,904,000) | 188,646,000 | |
| Amounts reclassified from accumulated other comprehensive loss for amortization of net losses | 35,110,000 | 36,994,000 | 72,611,000 | 73,242,000 | |
| Total other comprehensive income, net of tax | (14,537,000) | 85,411,000 | (2,293,000) | 261,888,000 | |
| Ending balance | $ (1,007,943,000) | $ (1,233,295,000) | $ (1,007,943,000) | $ (1,233,295,000) | |