Investments (Fixed Maturity and Equity Securities Available-For-Sale by Sector) (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	$ 286,069	$ 271,676
Cost or Amortized Cost	2,140	2,464
Gross Unrealized OTTI Loss	(41)	(8)	$ 76
Fixed maturity securities available-for-sale, at estimated fair value (amortized cost: $286,069 and $271,676, respectively)	308,931	289,563
Equity securities	2,513	2,894
Fixed Maturity Securities
Available-for-sale Securities [Abstract]
Gross Unrealized Gain	24,765	21,826
Gross Unrealized Temporary Loss	1,945	3,946
Gross Unrealized OTTI Loss	(42)	(7)
U.S. corporate
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	76,005	73,280
Gross Unrealized Gain	7,007	6,027
Gross Unrealized Temporary Loss	351	764
Gross Unrealized OTTI Loss	0	0
Fixed maturity securities available-for-sale, at estimated fair value (amortized cost: $286,069 and $271,676, respectively)	82,661	78,543
Foreign corporate
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	52,409	49,308
Gross Unrealized Gain	3,836	2,926
Gross Unrealized Temporary Loss	676	1,572
Gross Unrealized OTTI Loss	0	(1)
Fixed maturity securities available-for-sale, at estimated fair value (amortized cost: $286,069 and $271,676, respectively)	55,569	50,663
Foreign government
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	55,351	49,864
Gross Unrealized Gain	6,495	6,485
Gross Unrealized Temporary Loss	312	373
Gross Unrealized OTTI Loss	0	0
Fixed maturity securities available-for-sale, at estimated fair value (amortized cost: $286,069 and $271,676, respectively)	61,534	55,976
RMBS
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	27,846	28,393
Gross Unrealized Gain	1,145	1,039
Gross Unrealized Temporary Loss	233	410
Gross Unrealized OTTI Loss	(42)	(10)
Fixed maturity securities available-for-sale, at estimated fair value (amortized cost: $286,069 and $271,676, respectively)	28,800	29,032
U.S. government and agency
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	43,446	41,294
Gross Unrealized Gain	4,227	3,682
Gross Unrealized Temporary Loss	279	543
Gross Unrealized OTTI Loss	0	0
Fixed maturity securities available-for-sale, at estimated fair value (amortized cost: $286,069 and $271,676, respectively)	47,394	44,433
CMBS
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	8,047	7,294
Gross Unrealized Gain	222	237
Gross Unrealized Temporary Loss	42	71
Gross Unrealized OTTI Loss	0	0
Fixed maturity securities available-for-sale, at estimated fair value (amortized cost: $286,069 and $271,676, respectively)	8,227	7,460
ABS
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	12,213	11,266
Gross Unrealized Gain	116	90
Gross Unrealized Temporary Loss	39	128
Gross Unrealized OTTI Loss	(1)	3
Fixed maturity securities available-for-sale, at estimated fair value (amortized cost: $286,069 and $271,676, respectively)	12,291	11,225
State and political subdivision
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	10,752	10,977
Gross Unrealized Gain	1,717	1,340
Gross Unrealized Temporary Loss	13	85
Gross Unrealized OTTI Loss	1	1
Fixed maturity securities available-for-sale, at estimated fair value (amortized cost: $286,069 and $271,676, respectively)	12,455	12,231
Equity securities
Available-for-sale Securities [Abstract]
Gross Unrealized Gain	393	483
Gross Unrealized Temporary Loss	20	53
Gross Unrealized OTTI Loss	0	0
Equity securities	2,513	2,894
Common stock
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	1,687	1,827
Gross Unrealized Gain	364	464
Gross Unrealized Temporary Loss	16	13
Gross Unrealized OTTI Loss	0	0
Equity securities	2,035	2,278
Non-redeemable preferred stock
Available-for-sale Securities [Abstract]
Cost or Amortized Cost	453	637
Gross Unrealized Gain	29	19
Gross Unrealized Temporary Loss	4	40
Gross Unrealized OTTI Loss	0	0
Equity securities	$ 478	$ 616