Investments (Net Investment Income) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Net Investment Income [Line Items]
Less: Investment expenses	$ 293	$ 235	$ 820	$ 732
Subtotal	4,295	4,609	12,909	12,527
Securities Investment
Net Investment Income [Line Items]
Subtotal	4,354	4,315	12,865	12,636
Subtotal	4,061	4,080	12,045	11,904
Fixed maturity securities
Net Investment Income [Line Items]
Subtotal	2,869	2,906	8,528	8,838
Equity Securities
Net Investment Income [Line Items]
Subtotal	31	29	93	90
Actively traded securities and FVO general account securities
Net Investment Income [Line Items]
Subtotal	16	25	61	41
Mortgage loans
Net Investment Income [Line Items]
Subtotal	809	710	2,303	2,165
Policy loans
Net Investment Income [Line Items]
Subtotal	130	129	386	385
Real estate and real estate joint ventures
Net Investment Income [Line Items]
Subtotal	156	199	478	490
Other limited partnership interests
Net Investment Income [Line Items]
Subtotal	214	184	648	309
Cash, cash equivalents and short-term investments
Net Investment Income [Line Items]
Subtotal	52	38	159	112
Operating joint ventures
Net Investment Income [Line Items]
Subtotal	6	5	13	28
Other
Net Investment Income [Line Items]
Subtotal	71	90	196	178
FVO contractholder-directed unit-linked investments
Net Investment Income [Line Items]
Subtotal	$ 234	$ 529	$ 864	$ 623