Investments (Net Investment Income) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Net Investment Income [Line Items]
Less: Investment expenses	$ 315	$ 271	$ 617	$ 532
Subtotal	4,473	4,193	8,218	8,614
Securities Investment
Net Investment Income [Line Items]
Subtotal	4,502	4,250	8,902	8,516
Subtotal	4,187	3,979	8,285	7,984
Fixed maturity securities
Net Investment Income [Line Items]
Subtotal	3,014	2,839	5,910	5,664
Equity Securities
Net Investment Income [Line Items]
Subtotal	15	31	31	62
Actively Traded Securities At Estimated Fair Value And FVO Securities [Member]
Net Investment Income [Line Items]
Subtotal	8	16	14	45
Mortgage loans
Net Investment Income [Line Items]
Subtotal	815	758	1,607	1,494
Policy loans
Net Investment Income [Line Items]
Subtotal	127	129	251	256
Real Estate Investment [Member]
Net Investment Income [Line Items]
Subtotal	195	169	363	322
Real estate and real estate joint ventures
Net Investment Income [Line Items]
Subtotal	97	121	302	284
Other limited partnership interests
Net Investment Income [Line Items]
Subtotal	120	194	327	434
Cash, cash equivalents and short-term investments
Net Investment Income [Line Items]
Subtotal	95	56	167	107
Operating joint ventures
Net Investment Income [Line Items]
Subtotal	19	5	32	7
Other
Net Investment Income [Line Items]
Subtotal	94	53	200	125
FVO contractholder-directed unit-linked investments
Net Investment Income [Line Items]
Subtotal	$ 286	$ 214	$ (67)	$ 630