Investments (Fixed Maturity and Equity Securities Available-For-Sale by Sector) (Details) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Debt Securities, Available-for-sale [Abstract]
Cost or Amortized Cost	$ 293,268	$ 286,069
Gross Unrealized OTTI Loss	36	41
Debt Securities, Available-for-sale	304,840	308,931
Equity securities	$ 1,479	$ 2,513
Percentage of Available-for-sale Equity Securities	100.00%	100.00%
Fixed Maturity Securities
Debt Securities, Available-for-sale [Abstract]
Gross Unrealized Gain	$ 16,787	$ 24,765
Gross Unrealized Temporary Loss	5,251	1,945
Gross Unrealized OTTI Loss	(36)	(42)
CMBS
Debt Securities, Available-for-sale [Abstract]
Cost or Amortized Cost	8,763	8,047
Gross Unrealized Gain	86	222
Gross Unrealized Temporary Loss	141	42
Gross Unrealized OTTI Loss	0	0
Debt Securities, Available-for-sale	8,708	8,227
ABS
Debt Securities, Available-for-sale [Abstract]
Cost or Amortized Cost	12,775	12,213
Gross Unrealized Gain	79	116
Gross Unrealized Temporary Loss	38	39
Gross Unrealized OTTI Loss	1	(1)
Debt Securities, Available-for-sale	12,815	12,291
State and political subdivision
Debt Securities, Available-for-sale [Abstract]
Cost or Amortized Cost	10,548	10,752
Gross Unrealized Gain	1,147	1,717
Gross Unrealized Temporary Loss	95	13
Gross Unrealized OTTI Loss	0	1
Debt Securities, Available-for-sale	11,600	12,455
Residential Mortgage Backed Securities [Member]
Debt Securities, Available-for-sale [Abstract]
Cost or Amortized Cost	27,427	27,846
Gross Unrealized Gain	881	1,145
Gross Unrealized Temporary Loss	687	233
Gross Unrealized OTTI Loss	(37)	(42)
Debt Securities, Available-for-sale	27,658	28,800
Foreign corporate
Debt Securities, Available-for-sale [Abstract]
Cost or Amortized Cost	53,097	52,409
Gross Unrealized Gain	2,509	3,836
Gross Unrealized Temporary Loss	1,386	676
Gross Unrealized OTTI Loss	0	0
Debt Securities, Available-for-sale	54,220	55,569
Debt Security, Government, Non-US [Member]
Debt Securities, Available-for-sale [Abstract]
Cost or Amortized Cost	55,502	55,351
Gross Unrealized Gain	5,534	6,495
Gross Unrealized Temporary Loss	564	312
Gross Unrealized OTTI Loss	0	0
Debt Securities, Available-for-sale	60,472	61,534
U.S. government and agency
Debt Securities, Available-for-sale [Abstract]
Cost or Amortized Cost	43,830	43,446
Gross Unrealized Gain	2,506	4,227
Gross Unrealized Temporary Loss	764	279
Gross Unrealized OTTI Loss	0	0
Debt Securities, Available-for-sale	45,572	47,394
U.S. corporate
Debt Securities, Available-for-sale [Abstract]
Cost or Amortized Cost	81,326	76,005
Gross Unrealized Gain	4,045	7,007
Gross Unrealized Temporary Loss	1,576	351
Gross Unrealized OTTI Loss	0	0
Debt Securities, Available-for-sale	83,795	82,661
Equity Securities
Debt Securities, Available-for-sale [Abstract]
Equity securities	1,479	2,513
Non-redeemable preferred stock
Debt Securities, Available-for-sale [Abstract]
Equity securities	$ 416	$ 478
Percentage of Available-for-sale Equity Securities	28.10%	19.00%
Common Stock
Debt Securities, Available-for-sale [Abstract]
Equity securities	$ 1,063	$ 2,035
Percentage of Available-for-sale Equity Securities	71.90%	81.00%