Fair Value Measurements - The carrying value and fair value of financial instruments (Details) - USD ($) $ in Millions	Mar. 31, 2022	Dec. 31, 2021
Financial assets:
Mortgage loans	$ 784	$ 520
Long-term debt	1,917	1,964
Level 1
Financial assets:
Cash and cash equivalents	1,181	2,131
Mortgage loans	0	0
Total financial assets not accounted for at fair value	1,181	2,131
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	1,976	2,258
Total financial liabilities not accounted for at fair value	1,976	2,258
Level 3
Financial assets:
Cash and cash equivalents	0	0
Mortgage loans	768	533
Total financial assets not accounted for at fair value	768	533
Long-term debt	3	3
Total financial liabilities not accounted for at fair value	3	3
Carrying Value
Financial assets:
Cash and cash equivalents	1,181	2,131
Mortgage loans	784	520
Total financial assets not accounted for at fair value	1,965	2,651
Long-term debt	1,917	1,964
Total financial liabilities not accounted for at fair value	1,917	1,964
Fair Value
Financial assets:
Cash and cash equivalents	1,181	2,131
Mortgage loans	768	533
Total financial assets not accounted for at fair value	1,949	2,664
Long-term debt	1,979	2,261
Total financial liabilities not accounted for at fair value	$ 1,979	$ 2,261