Fair Value Measurements - The carrying value and fair value of financial instruments (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Financial assets:
Mortgage loans	$ 1,623	$ 1,329
Policy loans	151	164
Financial liabilities:
Long-term debt	1,963	1,473
Level 1
Financial assets:
Cash and cash equivalents	2,810	2,314
Mortgage loans	0	0
Policy loans	0	0
Total financial assets not accounted for at fair value	2,810	2,314
Financial liabilities:
Annuity benefits accumulated	0	0
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
Policy loans	0	0
Total financial assets not accounted for at fair value	0	0
Financial liabilities:
Annuity benefits accumulated	0	0
Long-term debt	2,322	1,619
Total financial liabilities not accounted for at fair value	2,322	1,619
Level 3
Financial assets:
Cash and cash equivalents	0	0
Mortgage loans	1,652	1,346
Policy loans	151	164
Total financial assets not accounted for at fair value	1,803	1,510
Financial liabilities:
Annuity benefits accumulated	43,081	40,182
Long-term debt	3	3
Total financial liabilities not accounted for at fair value	43,084	40,185
Carrying Value
Financial assets:
Cash and cash equivalents	2,810	2,314
Mortgage loans	1,623	1,329
Policy loans	151	164
Total financial assets not accounted for at fair value	4,584	3,807
Financial liabilities:
Annuity benefits accumulated	41,460	40,159
Long-term debt	1,963	1,473
Total financial liabilities not accounted for at fair value	43,423	41,632
Fair Value
Financial assets:
Cash and cash equivalents	2,810	2,314
Mortgage loans	1,652	1,346
Policy loans	151	164
Total financial assets not accounted for at fair value	4,613	3,824
Financial liabilities:
Annuity benefits accumulated	43,081	40,182
Long-term debt	2,325	1,622
Total financial liabilities not accounted for at fair value	$ 45,406	$ 41,804