Investments (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	$ 3,771	$ 3,782	$ 3,534
Less: Investment expenses	170	203	196
Net investment income	3,601	3,579	3,338
Fixed maturity securities
Net Investment Income [Line Items]
Gross investment income	2,700	2,673	2,565
Equity securities
Net Investment Income [Line Items]
Gross investment income	6	8	7
Mortgage loans
Net Investment Income [Line Items]
Gross investment income	666	680	543
Policy loans
Net Investment Income [Line Items]
Gross investment income	56	67	85
Limited partnerships and LLCs
Net Investment Income [Line Items]
Gross investment income	240	220	258
Cash, cash equivalents and short-term investments
Net Investment Income [Line Items]
Gross investment income	49	93	35
Other
Net Investment Income [Line Items]
Gross investment income	$ 54	$ 41	$ 41

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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