Fair Value Measurements - The carrying value and fair value of financial instruments (Details) - USD ($) $ in Millions		Dec. 31, 2019	Dec. 31, 2018
Financial assets:
Mortgage loans		$ 1,329	$ 1,068
Policy loans		164	174
Financial liabilities:
Long-term debt		1,473	1,302
Level 1
Financial assets:
Cash and cash equivalents		2,314	1,515
Mortgage loans		0	0
Policy loans		0	0
Total financial assets not accounted for at fair value		2,314	1,515
Financial liabilities:
Annuity benefits accumulated	[1]	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	[1]	0	0
Long-term debt		1,619	1,228
Total financial liabilities not accounted for at fair value		1,619	1,228
Level 3
Financial assets:
Cash and cash equivalents		0	0
Mortgage loans		1,346	1,056
Policy loans		164	174
Total financial assets not accounted for at fair value		1,510	1,230
Financial liabilities:
Annuity benefits accumulated	[1]	40,182	34,765
Long-term debt		3	3
Total financial liabilities not accounted for at fair value		40,185	34,768
Carrying Value
Financial assets:
Cash and cash equivalents		2,314	1,515
Mortgage loans		1,329	1,068
Policy loans		164	174
Total financial assets not accounted for at fair value		3,807	2,757
Financial liabilities:
Annuity benefits accumulated	[1]	40,159	36,384
Long-term debt		1,473	1,302
Total financial liabilities not accounted for at fair value		41,632	37,686
Fair Value
Financial assets:
Cash and cash equivalents		2,314	1,515
Mortgage loans		1,346	1,056
Policy loans		164	174
Total financial assets not accounted for at fair value		3,824	2,745
Financial liabilities:
Annuity benefits accumulated	[1]	40,182	34,765
Long-term debt		1,622	1,231
Total financial liabilities not accounted for at fair value		$ 41,804	$ 35,996

[1] Excludes $247 million and $232 million of life contingent annuities in the payout phase at December 31, 2019 and 2018, respectively.