Investments (Net Investment Income) (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Net Investment Income [Line Items]
Gross investment income	$ 3,782	$ 3,534	$ 3,256
Less: Investment expenses	203	196	178
Net investment income	3,579	3,338	3,078
Fixed maturity securities
Net Investment Income [Line Items]
Gross investment income	2,673	2,565	2,420
Equity securities
Net Investment Income [Line Items]
Gross investment income	8	7	9
Mortgage loans
Net Investment Income [Line Items]
Gross investment income	680	543	454
Policy loans
Net Investment Income [Line Items]
Gross investment income	67	85	73
Limited partnerships and LLCs
Net Investment Income [Line Items]
Gross investment income	220	258	237
Cash, cash equivalents and short-term investments
Net Investment Income [Line Items]
Gross investment income	93	35	35
Other
Net Investment Income [Line Items]
Gross investment income	$ 41	$ 41	$ 28

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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