Investments - Schedule of sources of net investment income (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Net Investment Income [Line Items]
Gross investment income	$ 2,161	$ 2,325	$ 2,116
Investment expenses	(29)	(22)	(22)
Net investment income	2,132	2,303	2,094
Fixed maturities
Net Investment Income [Line Items]
Gross investment income	1,880	1,915	1,742
Equity in earnings of partnerships and similar investments
Net Investment Income [Line Items]
Gross investment income	98	154	161
Other
Net Investment Income [Line Items]
Gross investment income	96	132	112
Investment income \| Equity securities
Net Investment Income [Line Items]
Gross investment income	63	85	79
Accounting Standards Update 2016-01 \| Equity securities
Net Investment Income [Line Items]
Gross investment income	$ 24	$ 39	$ 22

Amount, before investment expense, of income earned from investments in securities and real estate. Includes, but is not limited to, real estate investment, policy loans, dividends, and interest. Excludes realized gain (loss) on investments.

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Amount of expenses related to the generation of investment income.

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Amount, after investment expense, of income earned from investments in securities and real estate. Includes, but is not limited to, real estate investment, policy loans, dividends, and interest. Excludes realized gain (loss) on investments.

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