Trust Assets, Escrow and Other Deposits (Narrative) (Detail) - USD ($) $ in Millions |
Sep. 30, 2026 |
Dec. 31, 2025 |
|---|---|---|
| Other Assets [Line Items] | ||
| Escrow deposits | $ 10,000.0 | $ 9,300.0 |
| Assets held-in-trust | 6,100.0 | 5,600.0 |
| Like-kind exchange funds | 2,600.0 | 2,700.0 |
| Cash deposits | 2,100.0 | 1,600.0 |
| First American Trust | ||
| Other Assets [Line Items] | ||
| Escrow deposits | 4,100.0 | 3,700.0 |
| Assets held-in-trust | 155.2 | 173.9 |
| Cash deposits | 1,500.0 | 1,000.0 |
| FA Trust | ||
| Other Assets [Line Items] | ||
| Like-kind exchange funds | 1,100.0 | $ 93.6 |
| Mortgage Loan Subservicing Agreement | ||
| Other Assets [Line Items] | ||
| Fair value of debt securities on deposit | $ 52.2 |