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	$ 3,687	$ 3,428	$ 3,148
Less: Investment expenses	201	193	175
Net investment income	3,486	3,235	2,973
Fixed maturity securities
Net Investment Income [Line Items]
Gross investment income	2,627	2,499	2,347
Equity securities
Net Investment Income [Line Items]
Gross investment income	8	7	9
Mortgage loans
Net Investment Income [Line Items]
Gross investment income	676	538	450
Policy loans
Net Investment Income [Line Items]
Gross investment income	46	62	49
Limited partnerships and LLCs
Net Investment Income [Line Items]
Gross investment income	220	258	235
Cash, cash equivalents and short-term investments
Net Investment Income [Line Items]
Gross investment income	72	26	30
Other
Net Investment Income [Line Items]
Gross investment income	$ 38	$ 38	$ 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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