Fair Value Measurements - The carrying value and fair value of financial instruments (Details) - USD ($) $ in Millions	Dec. 31, 2024	Dec. 31, 2023
Financial assets:
Mortgage loans	$ 791	$ 643
Long-term debt	1,475	1,475
Level 1
Financial assets:
Cash and cash equivalents	1,406	1,225
Mortgage loans	0	0
Total financial assets not accounted for at fair value	1,406	1,225
Long-term debt	0	0
Total financial liabilities not accounted for at fair value	0	0
Level 2
Financial assets:
Cash and cash equivalents	0	0
Mortgage loans	0	0
Total financial assets not accounted for at fair value	0	0
Long-term debt	1,273	1,342
Total financial liabilities not accounted for at fair value	1,273	1,342
Level 3
Financial assets:
Cash and cash equivalents	0	0
Mortgage loans	754	596
Total financial assets not accounted for at fair value	754	596
Long-term debt	3	3
Total financial liabilities not accounted for at fair value	3	3
Carrying Value
Financial assets:
Cash and cash equivalents	1,406	1,225
Mortgage loans	791	643
Total financial assets not accounted for at fair value	2,197	1,868
Long-term debt	1,475	1,475
Total financial liabilities not accounted for at fair value	1,475	1,475
Fair Value
Financial assets:
Cash and cash equivalents	1,406	1,225
Mortgage loans	754	596
Total financial assets not accounted for at fair value	2,160	1,821
Long-term debt	1,276	1,345
Total financial liabilities not accounted for at fair value	$ 1,276	$ 1,345