Investments (Net Investment Income) (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Net Investment Income [Line Items]
Gross investment income	$ 954	$ 881	$ 2,762	$ 2,543
Less: Investment expenses	50	53	152	143
Net investment income	904	828	2,610	2,400
Fixed maturity securities
Net Investment Income [Line Items]
Gross investment income	654	624	1,962	1,857
Equity securities
Net Investment Income [Line Items]
Gross investment income	1	1	6	5
Mortgage loans
Net Investment Income [Line Items]
Gross investment income	172	137	505	381
Policy loans
Net Investment Income [Line Items]
Gross investment income	12	12	34	50
Real estate limited partnerships and limited liability companies
Net Investment Income [Line Items]
Gross investment income	12	12	32	36
Other limited partnership interests
Net Investment Income [Line Items]
Gross investment income	68	70	143	159
Cash, cash equivalents and short-term investments
Net Investment Income [Line Items]
Gross investment income	25	5	52	15
Other
Net Investment Income [Line Items]
Gross investment income	$ 10	$ 20	$ 28	$ 40

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, 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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