Investments (Net Investment Income) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Net Investment Income [Line Items]
Less: Investment expenses	$ 333	$ 293	$ 950	$ 820
Subtotal	4,486	4,295	12,704	12,909
Securities Investment
Net Investment Income [Line Items]
Subtotal	4,670	4,354	13,572	12,865
Subtotal	4,337	4,061	12,622	12,045
Fixed maturity securities
Net Investment Income [Line Items]
Subtotal	3,056	2,869	8,966	8,528
Equity Securities
Net Investment Income [Line Items]
Subtotal	15	31	46	93
Actively Traded Securities At Estimated Fair Value And FVO Securities [Member]
Net Investment Income [Line Items]
Subtotal	11	16	25	61
Mortgage loans
Net Investment Income [Line Items]
Subtotal	859	809	2,466	2,303
Policy loans
Net Investment Income [Line Items]
Subtotal	130	130	381	386
Real Estate Investment [Member]
Net Investment Income [Line Items]
Subtotal	175	156	538	478
Real estate and real estate joint ventures
Net Investment Income [Line Items]
Subtotal	180	164	482	448
Other limited partnership interests
Net Investment Income [Line Items]
Subtotal	227	214	554	648
Cash, cash equivalents and short-term investments
Net Investment Income [Line Items]
Subtotal	112	52	279	159
Operating joint ventures
Net Investment Income [Line Items]
Subtotal	2	6	34	13
Other
Net Investment Income [Line Items]
Subtotal	83	71	283	196
FVO contractholder-directed unit-linked investments
Net Investment Income [Line Items]
Subtotal	$ 149	$ 234	$ 82	$ 864