Investments - Net Investment Income (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income	$ 279	$ 203	$ 822	$ 550
Investment expenses	(11)	(8)	(28)	(25)
Net investment income (excluding net realized capital gains or losses)	268	195	794	525
Net realized capital gains (losses)	(22)	9	38	25
Net investment income	246	204	832	550
Yield-related impairment loss	3	2	35	44
Credit-related impairment loss	0	1	0	4
Supporting experience-rated products
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Net investment income	9	10	28	31
Debt securities
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income	157	151	474	441
Mortgage loans
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income	13	15	41	45
Other investments
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income	$ 109	$ 37	$ 307	$ 64

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