Investments (Net Investment Income) (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Net Investment Income [Line Items]
Gross investment income	$ 966	$ 828	$ 1,808	$ 1,662
Less: Investment expenses	48	48	102	90
Net investment income	918	780	1,706	1,572
Fixed maturity securities
Net Investment Income [Line Items]
Gross investment income	666	621	1,308	1,233
Equity securities
Net Investment Income [Line Items]
Gross investment income	2	2	5	4
Mortgage loans
Net Investment Income [Line Items]
Gross investment income	175	127	333	244
Policy loans
Net Investment Income [Line Items]
Gross investment income	12	28	22	38
Real estate limited partnerships and limited liability companies
Net Investment Income [Line Items]
Gross investment income	12	10	20	24
Other limited partnership interests
Net Investment Income [Line Items]
Gross investment income	75	24	75	89
Cash, cash equivalents and short-term investments
Net Investment Income [Line Items]
Gross investment income	17	5	27	10
Other
Net Investment Income [Line Items]
Gross investment income	$ 7	$ 11	$ 18	$ 20

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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